Devices and techniques for cutting and coagulating tissue

ABSTRACT

Various embodiments are directed to a method of driving an end effector coupled to an ultrasonic drive system of a surgical instrument. The method comprises generating at least one electrical signal. The at least one electrical signal is monitored against a first set of logic conditions. A first response is triggered when the first set of logic conditions is met. A parameter is determined from the at least one electrical signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application claiming priority under35 U.S.C. §120 to U.S. patent application Ser. No. 14/664,233, entitledDEVICES AND TECHNIQUES FOR CUTTING AND COAGULATING TISSUE, filed Mar.20, 2015, now U.S. Patent Application Publication No. 2015/0196318,which is a divisional application claiming priority under 35 U.S.C. §121to U.S. patent application Ser. No. 12/896,351, entitled DEVICE ANDTECHNIQUE FOR CUTTING AND COAGULATING TISSUE, filed Oct. 1, 2010, whichissued on Jul. 28, 2015 as U.S. Pat. No. 9,089,360, which is acontinuation-in-part application claiming priority under of 35 U.S.C.§120 to U.S. patent application Ser. No. 12/503,775, entitled ULTRASONICDEVICE FOR CUTTING AND COAGULATING WITH STEPPED OUTPUT, filed Jul. 15,2009, which issued on Nov. 15, 2011 as U.S. Pat. No. 8,058,771, whichclaims the benefit under Title 35, United States Code §119(e), of (1)U.S. Provisional Patent Application Ser. No. 61/086,619, entitledULTRASONIC DEVICE FOR CUTTING AND COAGULATING WITH STEPPED OUTPUT, filedAug. 6, 2008 and (2) U.S. Provisional Patent Application Ser. No.61/188,790, entitled ULTRASONIC DEVICE FOR CUTTING AND COAGULATING WITHSTEPPED OUTPUT, filed Aug. 13, 2008, the entire disclosures of which arehereby incorporated by reference herein.

U.S. patent application Ser. No. 12/896,351 also claims the benefitunder Title 35, United States Code §119(e), of U.S. Provisional PatentApplication Ser. No. 61/250,217, entitled A DUAL BIPOLAR AND ULTRASONICGENERATOR FOR ELECTRO-SURGICAL INSTRUMENTS, filed Oct. 9, 2009, theentire disclosure of which is hereby incorporated by reference herein.

TECHNICAL FIELD

The present disclosure generally relates to ultrasonic surgical systemsand, more particularly, to an ultrasonic system that allows surgeons toperform cutting and coagulation.

BACKGROUND

Ultrasonic surgical instruments are finding increasingly widespreadapplications in surgical procedures by virtue of the unique performancecharacteristics of such instruments. Depending upon specific instrumentconfigurations and operational parameters, ultrasonic surgicalinstruments can provide substantially simultaneous cutting of tissue andhemostasis by coagulation, desirably minimizing patient trauma. Thecutting action is typically realized by an-end effector, or blade tip,at the distal end of the instrument, which transmits ultrasonic energyto tissue brought into contact with the end effector. Ultrasonicinstruments of this nature can be configured for open surgical use,laparoscopic, or endoscopic surgical procedures includingrobotic-assisted procedures.

Some surgical instruments utilize ultrasonic energy for both precisecutting and controlled coagulation. Ultrasonic energy cuts andcoagulates by using lower temperatures than those used byelectrosurgery. Vibrating at high frequencies (e.g., 55,500 times persecond), the ultrasonic blade denatures protein in the tissue to form asticky coagulum. Pressure exerted on tissue with the blade surfacecollapses blood vessels and allows the coagulum to form a hemostaticseal. The precision of cutting and coagulation is controlled by thesurgeon's technique and adjusting the power level, blade edge, tissuetraction, and blade pressure.

A primary challenge of ultrasonic technology for medical devices,however, continues to be sealing of blood vessels. Work done by theapplicant and others has shown that optimum vessel sealing occurs whenthe inner muscle layer of a vessel is separated and moved away from theadventitia layer prior to the application of standard ultrasonic energy.Current efforts to achieve this separation have involved increasing theclamp force applied to the vessel.

Furthermore, the user does not always have visual feedback of the tissuebeing cut. Accordingly, it would be desirable to provide some form offeedback to indicate to the user that the cut is complete when visualfeedback is unavailable. Moreover, without some form of feedbackindicator to indicate that the cut is complete, the user may continue toactivate the harmonic instrument even though the cut is complete, whichcause possible damage to the harmonic instrument and surrounding tissueby the heat that is generated when activating a harmonic instrument withlittle to nothing between the jaws.

The ultrasonic transducer may be modeled as an equivalent circuit havingfirst branch comprising a static capacitance and a second “motional”branch comprising a serially connected inductance, resistance andcapacitance that defines the electromechanical properties of theresonator. Conventional ultrasonic generators may include a tuninginductor for tuning out the static capacitance at a resonant frequencyso that substantially all of generator's current output flows into themotional branch. The motional branch current, along with the drivevoltage, define the impedance and phase magnitude. Accordingly, using atuning inductor, the generator's current output represents the motionalbranch current, and the generator is thus able to maintain its driveoutput at the ultrasonic transducer's resonant frequency. The tuninginductor also transforms the phase impedance plot of the ultrasonictransducer to improve the generator's frequency lock capabilities.However, the tuning inductor must be matched with the specific staticcapacitance of an ultrasonic transducer. A different ultrasonictransducer having a different static capacitance requires a differenttuning inductor.

Electrosurgical devices for applying electrical energy to tissue inorder to treat and/or destroy the tissue are also finding increasinglywidespread applications in surgical procedures. An electrosurgicaldevice typically includes a handpiece, an instrument having adistally-mounted end effector (e.g., one or more electrodes). The endeffector can be positioned against the tissue such that electricalcurrent is introduced into the tissue. Electrosurgical devices can beconfigured for bipolar or monopolar operation. During bipolar operation,current is introduced into and returned from the tissue by active andreturn electrodes, respectively, of the end effector. During monopolaroperation, current is introduced into the tissue by an active electrodeof the end effector and returned through a return electrode (e.g., agrounding pad) separately located on a patient's body. Heat generated bythe current flowing through the tissue may form hemostatic seals withinthe tissue and/or between tissues and thus may be particularly usefulfor sealing blood vessels, for example. The end effector of anelectrosurgical device may also include a cutting member that is movablerelative to the tissue and the electrodes to transect the tissue.

Electrical energy applied by an electrosurgical device can betransmitted to the instrument by a generator in communication with thehandpiece. The electrical energy may be in the form of radio frequency(“RF”) energy. RF energy is a form of electrical energy that may be inthe frequency range of 300 kilohertz (kHz) to 1 megahertz (MHz). Inapplication, an electrosurgical device can transmit low frequency RFenergy through tissue, which causes ionic agitation, or friction, ineffect resistive heating, thereby increasing the temperature of thetissue. Because a sharp boundary is created between the affected tissueand the surrounding tissue, surgeons can operate with a high level ofprecision and control, without sacrificing un-targeted adjacent tissue.The low operating temperatures of RF energy is useful for removing,shrinking, or sculpting soft tissue while simultaneously sealing bloodvessels. RF energy works particularly well on connective tissue, whichis primarily comprised of collagen and shrinks when contacted by heat.

Due to their unique drive signal, sensing and feedback needs, ultrasonicand electrosurgical instruments have generally required dedicatedgenerators. Additionally, in cases where the instrument is disposable orinterchangeable with a handpiece, ultrasonic and electrosurgicalgenerators are limited in their ability to recognize the particularinstrument configuration being used and to optimize control anddiagnostic processes accordingly. Moreover, capacitive coupling ofsignals from the generator into patient-isolated circuits, especially incases of higher voltage and frequency ranges, may result in exposure ofa patient to unacceptable levels of leakage current.

It would be desirable to provide a surgical instrument that overcomessome of the deficiencies of current instruments. The surgical systemdescribed herein overcomes those deficiencies.

SUMMARY

One embodiment discloses a method of driving an end effector coupled toan ultrasonic drive system of a surgical instrument. The methodcomprises generating at least one electrical signal by a generator. Theat least one electrical signal is monitored against a first set of logicconditions. A first response of the generator is triggered when thefirst set of logic conditions is met. A parameter associated with thesurgical instrument is determined from the at least one electricalsignal.

FIGURES

The novel features of the described embodiments are set forth withparticularity in the appended claims. The described embodiments,however, both as to organization and methods of operation, may be bestunderstood by reference to the following description, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view illustrating one embodiment of anultrasonic surgical instrument.

FIG. 2 is an exploded perspective assembly view of one embodiment of anultrasonic surgical instrument.

FIG. 3 is a schematic of one embodiment of a clamp arm illustratingforce calculations.

FIG. 4 is a graphical representation of current, voltage, power,impedance, and frequency waveforms of a conventional oscillator at highpower and lightly loaded.

FIG. 5 is a graphical representation of current, voltage, power,impedance, and frequency waveforms of a conventional oscillator at highpower and heavily loaded.

FIG. 6 is a graphical representation of a current step function waveformand voltage, power, impedance, and frequency waveforms of one embodimentof an oscillator and unloaded.

FIG. 7 is a graphical representation of a current step function waveformand voltage, power, impedance, and frequency waveforms of one embodimentof an oscillator and lightly loaded.

FIG. 8 is a graphical representation of a current step function waveformand voltage, power, impedance, and frequency waveforms of one embodimentof an oscillator and heavily loaded.

FIG. 9 illustrates one embodiment of a drive system of a generator,which creates the ultrasonic electrical signal for driving an ultrasonictransducer.

FIG. 10 illustrates one embodiment of a surgical system comprising anultrasonic surgical instrument and a generator comprising a tissueimpedance module.

FIG. 11 illustrates one embodiment of a drive system of a generatorcomprising a tissue impedance module.

FIG. 12 illustrates one embodiment of a clamp arm assembly that may beemployed with a surgical system.

FIG. 13 is a schematic diagram of a tissue impedance module coupled to ablade and a clamp arm assembly with tissue located therebetween.

FIG. 14 illustrates one embodiment of a method for driving an endeffector coupled to an ultrasonic drive system of a surgical instrument.

FIG. 15A illustrates a logic flow diagram of one embodiment ofdetermining a change in tissue state and activating an output indicatoraccordingly.

FIG. 15B is a logic flow diagram illustrating one embodiment of theoperation of the frequency inflection point analysis module.

FIG. 15C is a logic flow diagram 900 illustrating one embodiment of theoperation of the voltage drop analysis module.

FIG. 16 illustrates one embodiment of a surgical system comprising agenerator and various surgical instruments usable therewith.

FIG. 17 is a diagram of the surgical system of FIG. 16.

FIG. 18 is a model illustrating motional branch current in oneembodiment.

FIG. 19 is a structural view of a generator architecture in oneembodiment.

FIG. 20 is a logic flow diagram of a tissue algorithm that may beimplemented in one embodiment of a generator.

FIG. 21 is a logic flow diagram of a signal evaluation tissue algorithmportion of the tissue algorithm shown in FIG. 20 that may be implementedin one embodiment of a generator.

FIG. 22 is a logic flow diagram for evaluating condition sets for thesignal evaluation tissue algorithm shown in FIG. 21 that may beimplemented in one embodiment of a generator.

FIG. 23 is a graphical representation of frequency slope (first timederivative of frequency) versus time waveform of one embodiment of agenerator during a typical tissue cut.

FIG. 23A is a graphical representation of slope of frequency slope(second time derivative of frequency) versus time waveform shown indashed line superimposed over the waveform shown in FIG. 23 of oneembodiment of a generator during a typical tissue cut.

FIG. 24 is a graphical representation of frequency versus time waveformof one embodiment of a generator during a typical tissue cut as itrelates to the graphical representation shown in FIG. 23.

FIG. 25 is a graphical representation of drive power versus timewaveform of one embodiment of a generator during a typical tissue cut asit relates to the graphical representation shown in FIG. 23.

FIG. 26 is a graphical representation of frequency slope versus timewaveform of one embodiment of a generator during a burn-in test.

FIG. 27 is a graphical representation of frequency versus time waveformof one embodiment of a generator during a burn-in test as it relates tothe graphical representation shown in FIG. 26.

FIG. 28 is a graphical representation of power consumption versus timewaveform of one embodiment of a generator during a burn-in test as itrelates to the graphical representation shown in FIG. 26.

FIG. 29 is a graphical representation of frequency change over timewaveform of several generator/instrument combinations during burn-intests.

FIG. 30 is a graphical representation of normalized combined impedance,current, frequency, power, energy, and temperature waveforms of oneembodiment of a generator coupled to an ultrasonic instrument to make 10successive cuts on excised porcine jejunum tissue as quickly as possiblewhile keeping the generator running throughout.

FIG. 31A is a graphical representation of impedance and current versustime waveforms of one embodiment of a generator during successive tissuecuts over a period of time.

FIG. 31B is a graphical representation of frequency versus time waveformof one embodiment of a generator during successive tissue cuts over aperiod of time.

FIG. 31C is a graphical representation of power, energy, and temperatureversus time waveforms of one embodiment of a generator during successivetissue cuts over a period of time.

FIG. 32 is a combined graphical representation of frequency, weightedfrequency slope waveform calculated via exponentially weighted movingaverage with an alpha value of 0.1, and temperature versus time waveformof one embodiment of a generator.

FIG. 33 is a graphical representation of a frequency versus timewaveform shown in FIG. 32.

FIG. 34 is a graphical representation of the weighted frequency slopeversus time waveform shown in FIG. 32.

FIG. 35 is a graphical representation of a frequency versus timewaveform of one embodiment of a generator over ten cuts on jejunumtissue and a graphical representation of a temperature versus timesignal.

FIG. 36 is a graphical representation of the frequency versus timewaveform shown in FIG. 35 of one embodiment of a generator over ten cutson jejunum tissue with activation of intervening tissue.

FIG. 37 is a graphical representation of a frequency slope versus timewaveform of one embodiment of a generator over ten cuts on jejunumtissue.

FIG. 38 is a graphical representation of a power versus time waveformrepresentative of power consumed by a one embodiment of a generator overten cuts on jejunum tissue.

FIG. 39 is a graphical representation of a current versus time waveformof one embodiment of a generator over ten cuts on jejunum tissue.

FIG. 40 is a graphical representation of a “cross-back frequency slopethreshold” parameter in connection with a frequency slope vs. timewaveform of one embodiment of a generator.

FIG. 41 is a combined graphical representation of a pulsed applicationof one embodiment of an ultrasonic instrument on an excised carotidartery showing normalized power, current, energy, and frequencywaveforms versus time.

FIG. 42A is a graphical representation of impedance and current versustime waveforms of one embodiment of a generator during successive tissuecuts over a period of time.

FIG. 42B is a graphical representation of a frequency versus timewaveform of one embodiment of a generator during successive tissue cutsover a period of time.

FIG. 42C is a graphical representation of power, energy, and temperatureversus time waveforms of one embodiment of a generator during successivetissue cuts over a period of time.

FIG. 43 is a graphical representation of a calculated frequency slopewaveform for the pulsed application shown in FIG. 41 and FIGS. 50A-Cplotted on a gross scale.

FIG. 44 is a zoomed in view of the graphical representation of thecalculated frequency slope waveform for the pulsed application shown inFIG. 43.

FIG. 45 is a graphical representation of other data waveforms ofinterest such as impedance, power, energy, temperature.

FIG. 46 is a graphical representation of a summary of weighted frequencyslope versus power level for various ultrasonic instrument types.

FIG. 47 is a graphical representation of resonant frequency, averagedresonant frequency, and frequency slope versus time waveforms of oneembodiment of a generator.

FIG. 48 is a zoomed in view of the resonant frequency and averagedresonant frequency versus time waveforms shown in FIG. 47.

FIG. 49 is a zoomed in view of the resonant frequency and current versustime waveforms of one embodiment of a generator.

FIG. 50 is a graphical representation of normalized combined power,impedance, current, energy, frequency, and temperature waveforms of oneembodiment of a generator coupled to an ultrasonic instrument.

DESCRIPTION

Before explaining various embodiments of ultrasonic surgical instrumentsin detail, it should be noted that the illustrative embodiments are notlimited in application or use to the details of construction andarrangement of parts illustrated in the accompanying drawings anddescription. The illustrative embodiments may be implemented orincorporated in other embodiments, variations and modifications, and maybe practiced or carried out in various ways. Further, unless otherwiseindicated, the terms and expressions employed herein have been chosenfor the purpose of describing the illustrative embodiments for theconvenience of the reader and are not for the purpose of limitationthereof.

Further, it is understood that any one or more of thefollowing-described embodiments, expressions of embodiments, examples,can be combined with any one or more of the other following-describedembodiments, expressions of embodiments, and examples.

Various embodiments are directed to improved ultrasonic surgicalinstruments configured for effecting tissue dissecting, cutting, and/orcoagulation during surgical procedures. In one embodiment, an ultrasonicsurgical instrument apparatus is configured for use in open surgicalprocedures, but has applications in other types of surgery, such aslaparoscopic, endoscopic, and robotic-assisted procedures. Versatile useis facilitated by selective use of ultrasonic energy.

The various embodiments will be described in combination with anultrasonic instrument as described herein. Such description is providedby way of example, and not limitation, and is not intended to limit thescope and applications thereof. For example, any one of the describedembodiments is useful in combination with a multitude of ultrasonicinstruments including those described in, for example, U.S. Pat. Nos.5,938,633; 5,935,144; 5,944,737; 5,322,055; 5,630,420; and 5,449,370.

As will become apparent from the following description, it iscontemplated that embodiments of the surgical instrument describedherein may be used in association with an oscillator unit of a surgicalsystem, whereby ultrasonic energy from the oscillator unit provides thedesired ultrasonic actuation for the present surgical instrument. It isalso contemplated that embodiments of the surgical instrument describedherein may be used in association with a signal generator unit of asurgical system, whereby electrical energy in the form of radiofrequencies (RF), for example, is used to provide feedback to the userregarding the surgical instrument. The ultrasonic oscillator and/or thesignal generator unit may be non-detachably integrated with the surgicalinstrument or may be provided as separate components, which can beelectrically attachable to the surgical instrument.

One embodiment of the present surgical apparatus is particularlyconfigured for disposable use by virtue of its straightforwardconstruction. However, it is also contemplated that other embodiments ofthe present surgical instrument can be configured for non-disposable ormultiple uses. Detachable connection of the present surgical instrumentwith an associated oscillator and signal generator unit is presentlydisclosed for single-patient use for illustrative purposes only.However, non-detachable integrated connection of the present surgicalinstrument with an associated oscillator and/or signal generator unit isalso contemplated. Accordingly, various embodiments of the presentlydescribed surgical instruments may be configured for single use and/ormultiple use with either detachable and/or non-detachable integraloscillator and/or signal generator unit, without limitation, and allcombinations of such configurations are contemplated to be within thescope of the present disclosure.

With reference to FIGS. 1-3, one embodiment of a surgical system 19including an ultrasonic surgical instrument 100 is illustrated. Thesurgical system 19 includes an ultrasonic generator 30 connected to anultrasonic transducer 50 via a suitable transmission medium such as acable 22, and an ultrasonic surgical instrument 100. Although in thepresently disclosed embodiment, the generator 30 is shown separate fromthe surgical instrument 100, in one embodiment, the generator 30 may beformed integrally with the surgical instrument 100 to form a unitarysurgical system 19. The generator 30 comprises an input device 406located on a front panel of the generator 30 console. The input device406 may comprise any suitable device that generates signals suitable forprogramming the operation of the generator 30 as subsequently describedwith reference to FIG. 9. Still with reference to FIGS. 1-3, the cable22 may comprise multiple electrical conductors for the application ofelectrical energy to positive (+) and negative (−) electrodes of theultrasonic transducer 50. It will be noted that, in some applications,the ultrasonic transducer 50 may be referred to as a “handle assembly”because the surgical instrument 100 of the surgical system 19 may beconfigured such that a surgeon may grasp and manipulate the ultrasonictransducer 50 during various procedures and operations. A suitablegenerator 30 is the GEN 300 sold by Ethicon Endo-Surgery, Inc. ofCincinnati, Ohio as is disclosed in one or more of the following U.S.patents, all of which are incorporated by reference herein: U.S. Pat.No. 6,480,796 (Method for Improving the Start Up of an Ultrasonic SystemUnder Zero Load Conditions); U.S. Pat. No. 6,537,291 (Method forDetecting a Loose Blade in a Handle Connected to an Ultrasonic SurgicalSystem); U.S. Pat. No. 6,626,926 (Method for Driving an UltrasonicSystem to Improve Acquisition of Blade Resonance Frequency at Startup);U.S. Pat. No. 6,633,234 (Method for Detecting Blade Breakage Using Rateand/or Impedance Information); U.S. Pat. No. 6,662,127 (Method forDetecting Presence of a Blade in an Ultrasonic System); U.S. Pat. No.6,678,621 (Output Displacement Control Using Phase Margin in anUltrasonic Surgical Handle); U.S. Pat. No. 6,679,899 (Method forDetecting Transverse Vibrations in an Ultrasonic Handle); U.S. Pat. No.6,908,472 (Apparatus and Method for Altering Generator Functions in anUltrasonic Surgical System); U.S. Pat. No. 6,977,495 (DetectionCircuitry for Surgical Handpiece System); U.S. Pat. No. 7,077,853(Method for Calculating Transducer Capacitance to Determine TransducerTemperature); U.S. Pat. No. 7,179,271 (Method for Driving an UltrasonicSystem to Improve Acquisition of Blade Resonance Frequency at Startup);and U.S. Pat. No. 7,273,483 (Apparatus and Method for Alerting GeneratorFunction in an Ultrasonic Surgical System).

In accordance with the described embodiments, the ultrasonic generator30 produces an electrical signal of a particular voltage, current, andfrequency, e.g., 55,500 cycles per second (Hz). The generator is 30connected by the cable 22 to the handle assembly 68, which containspiezoceramic elements forming the ultrasonic transducer 50. In responseto a switch 312 a on the handle assembly 68 or a foot switch 434connected to the generator 30 by another cable the generator signal isapplied to the transducer 50, which causes a longitudinal vibration ofits elements. A structure connects the transducer 50 to a surgical blade79, which is thus vibrated at ultrasonic frequencies when the generatorsignal is applied to the transducer 50. The structure is designed toresonate at the selected frequency, thus amplifying the motion initiatedby the transducer 50. In one embodiment, the generator 30 is configuredto produce a particular voltage, current, and/or frequency output signalthat can be stepped with high resolution, accuracy, and repeatability.

Referring to FIG. 4, in current systems a conventional oscillator isactivated at time 0 resulting in current 300 rising to a desired setpoint of approximately 340 mA. At approximately 2 seconds a light loadis applied resulting in corresponding increases to voltage 310, power320, impedance 330, and changes in resonant frequency 340.

Referring to FIG. 5, in current systems a conventional oscillator isactivated at time 0 resulting in the current 300 rising to a desired setpoint of approximately 340 mA. At approximately 2 seconds an increasingload is applied resulting in corresponding increases to the voltage 310,power 320, impedance 330, and changes in resonant frequency 340. Atapproximately 7 seconds, the load has increased to the point that theoscillator enters into a flat power mode where further increases in loadmaintain the power at 35 W as long as the oscillator stays withinvoltage limits of the power supply. The current 300 and therefore,displacement, varies during flat power mode. At approximately 11.5seconds, the load is reduced to the point where the current 300 returnsto the desired set point of approximately 340 mA. The voltage 310, power320, impedance 330, and resonant frequency 340 vary with the load.

With reference now back to FIGS. 1-3, the ultrasonic surgical instrument100 includes a multi-piece handle assembly 68 adapted to isolate theoperator from the vibrations of the acoustic assembly contained withinthe ultrasonic transducer 50. The handle assembly 68 can be shaped to beheld by a user in a conventional manner, but it is contemplated that thepresent ultrasonic surgical instrument 100 principally be grasped andmanipulated by a trigger-like arrangement provided by a handle assemblyof the instrument, as will be described. While a multi-piece handleassembly 68 is illustrated, the handle assembly 68 may comprise a singleor unitary component. The proximal end of the ultrasonic surgicalinstrument 100 receives and is fitted to the distal end of theultrasonic transducer 50 by insertion of the transducer 50 into thehandle assembly 68. In one embodiment, the ultrasonic surgicalinstrument 100 may be attached to and removed from the ultrasonictransducer 50 as a unit. In other embodiments, the ultrasonic surgicalinstrument 100 and the ultrasonic transducer 50 may be formed as anintegral unit. The ultrasonic surgical instrument 100 may include ahandle assembly 68, comprising a mating housing portion 69, a housingportion 70, and a transmission assembly 71. When the present instrumentis configured for endoscopic use, the construction can be dimensionedsuch that the transmission assembly 71 has an outside diameter ofapproximately 5.5 mm. The elongated transmission assembly 71 of theultrasonic surgical instrument 100 extends orthogonally from theinstrument handle assembly 68. The transmission assembly 71 can beselectively rotated with respect to the handle assembly 68 by a rotationknob 29 as further described below. The handle assembly 68 may beconstructed from a durable plastic, such as polycarbonate or a liquidcrystal polymer. It is also contemplated that the handle assembly 68 mayalternatively be made from a variety of materials including otherplastics, ceramics, or metals.

The transmission assembly 71 may include an outer tubular member or anouter sheath 72, an inner tubular actuating member 76, a waveguide 80,and an end effector 81 comprising, for example, the blade 79, a clamparm 56, and one or more clamp pads 58. As subsequently described, theouter sheath 72, the actuating member 76, and the waveguide 80 ortransmission rod may be joined together for rotation as a unit (togetherwith the ultrasonic transducer 50) relative to the handle assembly 68.The waveguide 80, which is adapted to transmit ultrasonic energy fromthe ultrasonic transducer 50 to the blade 79 may be flexible,semi-flexible, or rigid. The waveguide 80 also may be configured toamplify the mechanical vibrations transmitted through the waveguide 80to the blade 79 as is well known in the art. The waveguide 80 mayfurther have features to control the gain of the longitudinal vibrationalong the waveguide 80 and features to tune the waveguide 80 to theresonant frequency of the system. In particular, the waveguide 80 mayhave any suitable cross-sectional dimension. For example, the waveguide80 may have a substantially uniform cross-section or the waveguide 80may be tapered at various sections or may be tapered along its entirelength. In one expression of the current embodiment, the waveguidediameter is about 0.113 inches nominal to minimize the amount ofdeflection at the blade 79 so that gapping in the proximal portion ofthe end effector 81 is minimized.

The blade 79 may be integral with the waveguide 80 and formed as asingle unit. In an alternate expression of the current embodiment, theblade 79 may be connected by a threaded connection, a welded joint, orother coupling mechanisms. The distal end of the blade 79 is disposednear an anti-node in order to tune the acoustic assembly to a preferredresonant frequency f_(o) when the acoustic assembly is not loaded bytissue. When the ultrasonic transducer 50 is energized, the distal endof the blade 79 is configured to move longitudinally in the range of,for example, approximately 10 to 500 microns peak-to-peak, andpreferably in the range of about 20 to about 200 microns at apredetermined vibration frequency f_(o) of, for example, 55,500 Hz.

With particular reference to FIGS. 1-3, therein is illustrated oneembodiment of the clamp member 60 for use with the present ultrasonicsurgical instrument 100 and which is configured for cooperative actionwith the blade 79. The clamp member 60 in combination with the blade 79is commonly referred to as the end effector 81, and the clamp member 60is also commonly referred to as the jaw. The clamp member 60 includes apivotally movable clamp arm 56, which is connected to the distal end ofthe outer sheath 72 and the actuating member 76, in combination with atissue engaging pad or clamp pad 58. The clamp arm 56 is pivotallymovable by a trigger 34 and the end effector 81 is rotatably movable bythe rotation knob 29. In one expression of the embodiment, the clamp pad58 is formed from TEFLON® a trademark name of E. I. Du Pont de Nemoursand Company, a low coefficient of friction polymer material, or anyother suitable low-friction material. The clamp pad 58 mounts on theclamp arm 56 for cooperation with the blade 79, with pivotal movement ofthe clamp arm 56 positioning the clamp pad 58 in substantially parallelrelationship to, and in contact with, the blade 79, thereby defining atissue treatment region. By this construction, tissue is grasped betweenthe clamp pad 58 and the blade 79. As illustrated, the clamp pad 58 maybe provided with a non-smooth surface, such as a saw tooth-likeconfiguration to enhance the gripping of tissue in cooperation with theblade 79. The saw tooth-like configuration, or teeth, provide tractionagainst the movement of the blade 79. The teeth also provide countertraction to the blade 79 and clamping movement. As would be appreciatedby one skilled in the art, the saw tooth-like configuration is just oneexample of many tissue engaging surfaces to prevent movement of thetissue relative to the movement of the blade 79. Other illustrativeexamples include bumps, criss-cross patterns, tread patterns, a bead, orsand blasted surface.

Due to sinusoidal motion, the greatest displacement or amplitude ofmotion is located at the most distal portion of the blade 79, while theproximal portion of the tissue treatment region is on the order of 50%of the distal tip amplitude. During operation, the tissue in theproximal region of the end effector 81 will desiccate and thin, and thedistal portion of the end effector 81 will transect tissue in thatdistal region, thereby allowing the desiccated and thinned tissue withinthe proximal region to slide distally into the more active region of theend effector 81 to complete the tissue transection.

FIG. 3 illustrates a force diagram and the relationship between theactuation force F_(A) (provided by the actuating member 76) andtransection force F_(T) (measured at the midpoint of the optimal tissuetreatment area).

F _(T) =F _(A)(X ₂ /X ₁)  (1)

Where F_(A) equals the spring preload of a proximal spring 94 (lessfrictional losses), which, in one embodiment, is about 12.5 pounds, andF_(T) equals about 4.5 pounds.

F_(T) is measured in the region of the clamp arm/blade interface whereoptimal tissue treatment occurs as defined by tissue marks 61 a and 61b. The tissue marks 61 a, b are etched or raised on the clamp arm 56 toprovide a visible mark to the surgeon so the surgeon has a clearindication of the optimal tissue treatment area. The tissue marks 61 a,b are about 7 mm apart in distance, and more preferably about 5 mm apartin distance.

FIG. 9 illustrates one embodiment of a drive system 32 of the generator30, which creates an ultrasonic electrical signal for driving anultrasonic transducer. The drive system 32 is flexible and can create anultrasonic electrical drive signal 416 at a desired frequency and powerlevel setting for driving the ultrasonic transducer 50. In variousembodiments, the generator 30 may comprise several separate functionalelements, such as modules and/or blocks. Although certain modules and/orblocks may be described by way of example, it can be appreciated that agreater or lesser number of modules and/or blocks may be used and stillfall within the scope of the embodiments. Further, although variousembodiments may be described in terms of modules and/or blocks tofacilitate description, such modules and/or blocks may be implemented byone or more hardware components, e.g., processors, Digital SignalProcessors (DSPs), Programmable Logic Devices (PLDs), ApplicationSpecific Integrated Circuits (ASICs), circuits, registers and/orsoftware components, e.g., programs, subroutines, logic and/orcombinations of hardware and software components.

In one embodiment, the generator 30 drive system 32 may comprise one ormore embedded applications implemented as firmware, software, hardware,or any combination thereof. The generator 30 drive system 32 maycomprise various executable modules such as software, programs, data,drivers, application program interfaces (APIs), and so forth. Thefirmware may be stored in nonvolatile memory (NVM), such as inbit-masked read-only memory (ROM) or flash memory. In variousimplementations, storing the firmware in ROM may preserve flash memory.The NVM may comprise other types of memory including, for example,programmable ROM (PROM), erasable programmable ROM (EPROM), electricallyerasable programmable ROM (EEPROM), or battery backed random-accessmemory (RAM) such as dynamic RAM (DRAM), Double-Data-Rate DRAM (DDRAM),and/or synchronous DRAM (SDRAM).

In one embodiment, the generator 30 drive system 32 comprises a hardwarecomponent implemented as a processor 400 for executing programinstructions for monitoring various measurable characteristics of theultrasonic surgical instrument 100 (FIG. 1) and generating a stepfunction output signal for driving the ultrasonic transducer 50 incutting and/or coagulation operating modes. It will be appreciated bythose skilled in the art that the generator 30 and the drive system 32may comprise additional or fewer components and only a simplifiedversion of the generator 30 and the drive system 32 are described hereinfor conciseness and clarity. In various embodiments, as previouslydiscussed, the hardware component may be implemented as a DSP, PLD,ASIC, circuits, and/or registers. In one embodiment, the processor 400may be configured to store and execute computer software programinstructions to generate the step function output signals for drivingvarious components of the ultrasonic surgical instrument 100, such asthe transducer 50, the end effector 81, and/or the blade 79.

In one embodiment, under control of one or more software programroutines, the processor 400 executes the methods in accordance with thedescribed embodiments to generate a step function formed by a stepwisewaveform of drive signals comprising current (I), voltage (V), and/orfrequency (f) for various time intervals or periods (T). The stepwisewaveforms of the drive signals may be generated by forming a piecewiselinear combination of constant functions over a plurality of timeintervals created by stepping the generator 30 drive signals, e.g.,output drive current (I), voltage (V), and/or frequency (f). The timeintervals or periods (T) may be predetermined (e.g., fixed and/orprogrammed by the user) or may be variable. Variable time intervals maybe defined by setting the drive signal to a first value and maintainingthe drive signal at that value until a change is detected in a monitoredcharacteristic. Examples of monitored characteristics may comprise, forexample, transducer impedance, tissue impedance, tissue heating, tissuetransection, tissue coagulation, and the like. The ultrasonic drivesignals generated by the generator 30 include, without limitation,ultrasonic drive signals capable of exciting the ultrasonic transducer50 in various vibratory modes such as, for example, the primarylongitudinal mode and harmonics thereof as well flexural and torsionalvibratory modes.

In one embodiment, the executable modules comprise one or more stepfunction algorithm(s) 402 stored in memory that when executed causes theprocessor 400 to generate a step function formed by a stepwise waveformof drive signals comprising current (I), voltage (V), and/or frequency(f) for various time intervals or periods (T). The stepwise waveforms ofthe drive signals may be generated by forming a piecewise linearcombination of constant functions over two or more time intervalscreated by stepping the generator's 30 output drive current (I), voltage(V), and/or frequency (f). The drive signals may be generated either forpredetermined fixed time intervals or periods (T) of time or variabletime intervals or periods of time in accordance with the one or morestepped output algorithm(s) 402. Under control of the processor 400, thegenerator 30 steps (e.g., increment or decrement) the current (I),voltage (V), and/or frequency (f) up or down at a particular resolutionfor a predetermined period (T) or until a predetermined condition isdetected, such as a change in a monitored characteristic (e.g.,transducer impedance, tissue impedance). The steps can change inprogrammed increments or decrements. If other steps are desired, thegenerator 30 can increase or decrease the step adaptively based onmeasured system characteristics.

In operation, the user can program the operation of the generator 30using the input device 406 located on the front panel of the generator30 console. The input device 406 may comprise any suitable device thatgenerates signals 408 that can be applied to the processor 400 tocontrol the operation of the generator 30. In various embodiments, theinput device 406 includes buttons, switches, thumbwheels, keyboard,keypad, touch screen monitor, pointing device, remote connection to ageneral purpose or dedicated computer. In other embodiments, the inputdevice 406 may comprise a suitable user interface. Accordingly, by wayof the input device 406, the user can set or program the current (I),voltage (V), frequency (f), and/or period (T) for programming the stepfunction output of the generator 30. The processor 400 then displays theselected power level by sending a signal on line 410 to an outputindicator 412.

In various embodiments, the output indicator 412 may provide visual,audible, and/or tactile feedback to the surgeon to indicate the statusof a surgical procedure, such as, for example, when tissue cutting andcoagulating is complete based on a measured characteristic of theultrasonic surgical instrument 100, e.g., transducer impedance, tissueimpedance, or other measurements as subsequently described. By way ofexample, and not limitation, visual feedback comprises any type ofvisual indication device including incandescent lamps or light emittingdiodes (LEDs), graphical user interface, display, analog indicator,digital indicator, bar graph display, digital alphanumeric display. Byway of example, and not limitation, audible feedback comprises any typeof buzzer, computer generated tone, computerized speech, voice userinterface (VUI) to interact with computers through a voice/speechplatform. By way of example, and not limitation, tactile feedbackcomprises any type of vibratory feedback provided through the instrumenthousing handle assembly 68.

In one embodiment, the processor 400 may be configured or programmed togenerate a digital current signal 414 and a digital frequency signal418. These signals 414, 418 are applied to a direct digital synthesizer(DDS) circuit 420 to adjust the amplitude and the frequency (f) of thecurrent output signal 416 to the transducer 50. The output of the DDScircuit 420 is applied to an amplifier 422 whose output is applied to atransformer 424. The output of the transformer 424 is the signal 416applied to the ultrasonic transducer 50, which is coupled to the blade79 by way of the waveguide 80 (FIG. 2).

In one embodiment, the generator 30 comprises one or more measurementmodules or components that may be configured to monitor measurablecharacteristics of the ultrasonic instrument 100 (FIG. 1). In theillustrated embodiment, the processor 400 may be employed to monitor andcalculate system characteristics. As shown, the processor 400 measuresthe impedance Z of the transducer 50 by monitoring the current suppliedto the transducer 50 and the voltage applied to the transducer 50. Inone embodiment, a current sense circuit 426 is employed to sense thecurrent flowing through the transducer 50 and a voltage sense circuit428 is employed to sense the output voltage applied to the transducer50. These signals may be applied to the analog-to-digital converter 432(ADC) via an analog multiplexer 430 circuit or switching circuitarrangement. The analog multiplexer 430 routes the appropriate analogsignal to the ADC 432 for conversion. In other embodiments, multipleADCs 432 may be employed for each measured characteristic instead of themultiplexer 430 circuit. The processor 400 receives the digital output433 of the ADC 432 and calculates the transducer impedance Z based onthe measured values of current and voltage. The processor 400 adjuststhe output drive signal 416 such that it can generate a desired powerversus load curve. In accordance with programmed step functionalgorithms 402, the processor 400 can step the drive signal 416, e.g.,the current or frequency, in any suitable increment or decrement inresponse to the transducer impedance Z.

To actually cause the surgical blade 79 to vibrate, e.g., actuate theblade 79, the user activates the foot switch 434 (FIG. 1) or the switch312 a (FIG. 1) on the handle assembly 68. This activation outputs thedrive signal 416 to the transducer 50 based on programmed values ofcurrent (I), frequency (f), and corresponding time periods (T). After apredetermined fixed time period (T), or variable time period based on ameasurable system characteristic such as changes in the impedance Z ofthe transducer 50, the processor 400 changes the output current step orfrequency step in accordance with the programmed values. The outputindicator 412 communicates the particular state of the process to theuser.

The programmed operation of the generator 30 can be further illustratedwith reference to FIGS. 6, 7, and 8, where graphical representations ofcurrent 300, voltage 310, power 320, impedance 330, and frequency 340are shown for the generator 30 in an unloaded state, a lightly loadedstate, and a heavily loaded state, respectively. FIG. 6 is a graphicalrepresentation of current 300, voltage 310, power 320, impedance 330,and frequency 340 waveforms of one embodiment of the generator 30 in anunloaded state. In the illustrated embodiment, the current 300 output ofthe generator 30 is stepped. As shown in FIG. 6, the generator 30 isinitially activated at about time 0 resulting in the current 300 risingto a first set point I₁ of about 100 mA. The current 300 is maintainedat the first set point I₂ for a first period T₁. At the end of the firstperiod T₁, e.g., about 1 second in the illustrated embodiment, thecurrent 300 set point I₁ is changed, e.g., stepped, by the generator 30in accordance with the software, e.g., the step function algorithm(s)402, to a second set point I₂ of about 175 mA for a second period T₂,e.g., about 2 seconds in the illustrated embodiment. At the end of thesecond period T₂, e.g., at about 3 seconds in the illustratedembodiment, the generator 30 software changes the current 300 to a thirdset point I₃ of about 350 mA. The voltage 310, current 300, power 320,and frequency respond only slightly because there is no load on thesystem.

FIG. 7 is a graphical representation of the current 300, voltage 310,power 320, impedance 330, and frequency 340 waveforms of one embodimentof the generator 30 under a lightly loaded state. Referring to FIG. 7,the generator 30 is activated at about time 0 resulting in the current300 rising to the first current 300 set point I₁ of about 100 mA. Atabout 1 second the current 300 set point is changed within the generator30 by the software to I₂ of about 175 mA, and then again at about 3seconds the generator 30 changes the current 300 set point to I₃ ofabout 350 mA. The voltage 310, current 300, power 320, and frequency 340are shown responding to the light load similar to that shown in FIG. 4.

FIG. 8 is a graphical representation of the current 300, voltage 310,power 320, impedance 330, and frequency 340 waveforms of one embodimentof the generator 30 under a heavily loaded state. Referring to FIG. 8,the generator 30 is activated at about time 0 resulting in the current300 rising to the first set point I₁ of about 100 mA. At about 1 secondthe current 300 set point is changed within the generator 30 by thesoftware to I₂ of about 175 mA, and then again at about 3 seconds thegenerator 30 changes the current 300 set point to I₃ of about 350 mA.The voltage 310, current 300, power 320, and frequency 340 are shownresponding to the heavy load similar to that shown in FIG. 5.

It will be appreciated by those skilled in the art that the current 300step function set points (e.g., I₁, I₂, I₃) and the time intervals orperiods (e.g., T₁, T₂) of duration for each of the step function setpoints described in FIGS. 6-8 are not limited to the values describedherein and may be adjusted to any suitable value as may be desired for agiven set of surgical procedures. Additional or fewer current set pointsand periods of duration may be selected as may be desired for a givenset of design characteristics or performance constraints. As previouslydiscussed, the periods may be predetermined by programming or may bevariable based on measurable system characteristics. The embodiments arenot limited in this context.

Having described operational details of various embodiments of thesurgical system 19, operations for the above surgical system 19 may befurther described in terms of a process for cutting and coagulating ablood vessel employing a surgical instrument comprising the input device406 and the transducer impedance measurement capabilities described withreference to FIG. 9. Although a particular process is described inconnection with the operational details, it can be appreciated that theprocess merely provides an example of how the general functionalitydescribed herein can be implemented by the surgical system 19. Further,the given process does not necessarily have to be executed in the orderpresented herein unless otherwise indicated. As previously discussed,the input device 406 may be employed to program the stepped output(e.g., current, voltage, frequency) to the ultrasonic transducer50/blade 79 assembly.

Accordingly, with reference now to FIGS. 1-3 and 6-9, one technique forsealing a vessel includes separating and moving the inner muscle layerof the vessel away from the adventitia layer prior to the application ofstandard ultrasonic energy to transect and seal the vessel. Althoughconventional methods have achieved this separation by increasing theforce applied to the clamp member 60, disclosed is an alternativeapparatus and method for cutting and coagulating tissue without relyingon clamp force alone. In order to more effectively separate the tissuelayers of a vessel, for example, the generator 30 may be programmed toapply a frequency step function to the ultrasonic transducer 50 tomechanically displace the blade 79 in multiple modes in accordance withthe step function. In one embodiment, the frequency step function may beprogrammed by way of the user interface 406, wherein the user can selecta stepped-frequency program, the frequency (f) for each step, and thecorresponding time period (T) of duration for each step for which theultrasonic transducer 50 will be excited. The user may program acomplete operational cycle by setting multiple frequencies for multipleperiods to perform various surgical procedures.

In one embodiment, a first ultrasonic frequency may be set initially tomechanically separate the muscle tissue layer of a vessel prior toapplying a second ultrasonic frequency to cut and seal the vessel. Byway of example, and not limitation, in accordance with oneimplementation of the program, initially, the generator 30 is programmedto output a first drive frequency f₁ for a first period T₁ of time (forexample less than approximately 1 second), wherein the first frequencyf₁ is significantly off resonance, for example, f_(o)/2, 2f_(o) or otherstructural resonant frequencies, where f_(o) is the resonant frequency(e.g., 55.5 kHz). The first frequency f₁ provides a low level ofmechanical vibration action to the blade 79 that, in conjunction withthe clamp force, mechanically separates the muscle tissue layer(subtherapeutic) of the vessel without causing significant heating thatgenerally occurs at resonance. After the first period T₁, the generator30 is programmed to automatically switch the drive frequency to theresonant frequency f_(o) for a second period T₂ to transect and seal thevessel. The duration of the second period T₂ may be programmed or may bedetermined by the length of time it actually takes to cut and seal thevessel as determined by the user or may be based on measured systemcharacteristics such as the transducer impedance Z as described in moredetail below.

In one embodiment, the tissue/vessel transection process (e.g.,separating the muscle layer of the vessel from the adventitia layer andtransecting/sealing the vessel) may be automated by sensing theimpedance Z characteristics of the transducer 50 to detect when thetransection of the tissue/vessel occurs. The impedance Z can becorrelated to the transection of the muscle layer and to thetransection/sealing of the vessel to provide a trigger for the processor400 to generate the frequency and/or current step function output. Aspreviously discussed with reference to FIG. 9, the impedance Z of thetransducer 50 may be calculated by the processor 400 based on thecurrent flowing through transducer 50 and the voltage applied to thetransducer 50 while the blade 79 is under various loads. Because theimpedance Z of the transducer 50 is proportional to the load applied tothe blade 79, as the load on the blade 79 increases, the impedance Z ofthe transducer 50 increases, and as the load on the blade 79 decreasesthe impedance Z of the transducer 50 decreases. Accordingly, theimpedance Z of the transducer 50 can be monitored to detect thetransection of the inner muscle tissue layer of the vessel from theadventitia layer and can also be monitored to detect when the vessel hasbeen transected and sealed.

In one embodiment, the ultrasonic surgical instrument 110 may beoperated in accordance with a programmed step function algorithmresponsive to the transducer impedance Z. In one embodiment, a frequencystep function output may be initiated based on a comparison of thetransducer impedance Z and one or more predetermined thresholds thathave been correlated with tissue loads against the blade 79. When thetransducer impedance Z transitions above or below (e.g., crosses) athreshold, the processor 400 applies a digital frequency signal 418 tothe DDS circuit 420 to change the frequency of the drive signal 416 by apredetermined step in accordance with the step function algorithm(s) 402responsive to the transducer impedance Z. In operation, the blade 79 isfirst located at the tissue treatment site. The processor 400 applies afirst digital frequency signal 418 to set a first drive frequency f1that is off resonance (e.g., f_(o)/2, 2f_(o) or other structuralresonant frequencies, where f_(o) is the resonant frequency). The drivesignal 416 is applied to the transducer 50 in response to activation ofthe switch 312 a on the handle assembly 68 or the foot switch 434.During this period the ultrasonic transducer 50 mechanically activatesthe blade 79 at the first drive frequency f₁. A force or load may beapplied to the clamp member 60 and the blade 79 to facilitate thisprocess. During this period, the processor 400 monitors the transducerimpedance Z until the load on the blade 79 changes and the transducerimpedance Z crosses a predetermined threshold to indicate that thetissue layer has been transected. The processor 400 then applies asecond digital frequency signal 418 to set a second drive frequency f₂,e.g., the resonant frequency f_(o) or other suitable frequency fortransecting, coagulating, and sealing tissue. Another portion of thetissue (e.g., the vessel) is then grasped between the clamp member 60and the blade 79. The transducer 50 is now energized by the drive signal416 at the second drive frequency f₂ by actuating either the foot switch434 or the switch 312 a on the handle assembly 68. It will beappreciated by those skilled in the art that the drive current (I)output also may be stepped as described with reference to FIGS. 6-8based on the transducer impedance Z.

According to one step function algorithm 402, the processor 400initially sets a first drive frequency f₁ that is significantly offresonance to separate the inner muscle layer of the vessel from theadventitia layer. During this period of operation the processor 400monitors the transducer impedance Z to determine when the inner musclelayer is transected or separated from the adventitia layer. Because thetransducer impedance Z is correlated to the load applied to the blade79, for example, cutting more tissue decrease the load on the blade 79and the transducer impedance Z. The transection of the inner musclelayer is detected when the transducer impedance Z drops below apredetermined threshold. When the change in transducer impedance Zindicates that the vessel has been separated from the inner musclelayer, the processor 400 sets the drive frequency to the resonantfrequency f_(o). The vessel is then grasped between the blade 79 and theclamp member 60 and the transducer 50 is activated by actuating eitherthe foot switch or the switch on the handle assembly 68 to transect andseal the vessel. In one embodiment, the impedance Z change may rangebetween about 1.5 to about 4 times a base impedance measurements from aninitial point of contact with the tissue to a point just before themuscle layer is transected and sealed.

FIG. 10 illustrates one embodiment of a surgical system 190 comprisingan ultrasonic surgical instrument 120 and a generator 500 comprising atissue impedance module 502. Although in the presently disclosedembodiment, the generator 500 is shown separate from the surgicalinstrument 120, in one embodiment, the generator 500 may be formedintegrally with the surgical instrument 120 to form a unitary surgicalsystem 190. In one embodiment, the generator 500 may be configured tomonitor the electrical impedance of the tissue Z_(t) and to control thecharacteristics of time and power level based on the tissue impedanceZ_(t). In one embodiment, the tissue impedance Z_(t) may be determinedby applying a subtherapeutic radio frequency (RF) signal to the tissueand measuring the current through the tissue by way of a returnelectrode on the clamp member 60. In the embodiment illustrated in FIG.10, an end effector 810 portion of the surgical system 190 comprises aclamp arm assembly 451 connected to the distal end of the outer sheath72. The blade 79 forms a first (e.g., energizing) electrode and theclamp arm assembly 451 comprises an electrically conductive portion thatforms a second (e.g., return) electrode. The tissue impedance module 502is coupled to the blade 79 and the clamp arm assembly 451 through asuitable transmission medium such as a cable 504. The cable 504comprises multiple electrical conductors for applying a voltage to thetissue and providing a return path for current flowing through thetissue back to the impedance module 502. In various embodiments, thetissue impedance module 502 may be formed integrally with the generator500 or may be provided as a separate circuit coupled to the generator500 (shown in phantom to illustrate this option). The generator 500 issubstantially similar to the generator 30 with the added feature of thetissue impedance module 502.

FIG. 11 illustrates one embodiment of a drive system 321 of thegenerator 500 comprising the tissue impedance module 502. The drivesystem 321 generates the ultrasonic electrical drive signal 416 to drivethe ultrasonic transducer 50. In one embodiment, the tissue impedancemodule 502 may be configured to measure the impedance Z_(t) of tissuegrasped between the blade 79 and the clamp arm assembly 451. The tissueimpedance module 502 comprises an RF oscillator 506, a voltage sensingcircuit 508, and a current sensing circuit 510. The voltage and currentsensing circuits 508, 510 respond to the RF voltage v_(rf) applied tothe blade 79 electrode and the RF current i_(rf) flowing through theblade 79 electrode, the tissue, and the conductive portion of the clamparm assembly 451. The sensed voltage v_(rf) and current i_(rf) areconverted to digital form by the ADC 432 via the analog multiplexer 430.The processor 400 receives the digitized output 433 of the ADC 432 anddetermines the tissue impedance Z_(t) by calculating the ratio of the RFvoltage v_(rf) to current i_(rf) measured by the voltage sense circuit508 and the current sense circuit 510. In one embodiment, thetransection of the inner muscle layer and the tissue may be detected bysensing the tissue impedance Z_(t). Accordingly, detection of the tissueimpedance Z_(t) may be integrated with an automated process forseparating the inner muscle layer from the outer adventitia layer priorto transecting the tissue without causing a significant amount ofheating, which normally occurs at resonance.

FIG. 12 illustrates one embodiment of the clamp arm assembly 451 thatmay be employed with the surgical system 190 (FIG. 10). In theillustrated embodiment, the clamp arm assembly 451 comprises aconductive jacket 472 mounted to a base 449. The conductive jacket 472is the electrically conductive portion of the clamp arm assembly 451that forms the second, e.g., return, electrode. In one implementation,the clamp arm 56 (FIG. 3) may form the base 449 on which the conductivejacket 472 is mounted. In various embodiments, the conductive jacket 472may comprise a center portion 473 and at least one downwardly-extendingsidewall 474 which can extend below the bottom surface 475 of the base449. In the illustrated embodiment, the conductive jacket 472 has twosidewalls 474 extending downwardly on opposite sides of the base 449. Inother embodiments, the center portion 473 may comprise at least oneaperture 476 which can be configured to receive a projection 477extending from the base 449. In such embodiments, the projections 477can be press-fit within the apertures 476 in order to secure theconductive jacket 472 to the base 449. In other embodiments, theprojections 477 can be deformed after they are inserted into theapertures 476. In various embodiments, fasteners can be used to securethe conductive jacket 472 to the base 449.

In various embodiments, the clamp arm assembly 451 may comprise anon-electrically conductive or insulative material, such as plasticand/or rubber, for example, positioned intermediate the conductivejacket 472 and the base 449. The electrically insulative material canprevent current from flowing, or shorting, between the conductive jacket472 and the base 449. In various embodiments, the base 449 may compriseat least one aperture 478, which can be configured to receive a pivotpin (not illustrated). The pivot pin can be configured to pivotablymount the base 449 to the sheath 72 (FIG. 10), for example, such thatthe clamp arm assembly 451 can be rotated between open and closedpositions relative to the sheath 72. In the illustrated embodiment, thebase 449 includes two apertures 478 positioned on opposite sides of thebase 449. In one embodiment, a pivot pin may be formed of or maycomprise a non-electrically conductive or insulative material, such asplastic and/or rubber, for example, which can be configured to preventcurrent from flowing into the sheath 72 even if the base 449 is inelectrical contact with the conductive jacket 472, for example.Additional clamp arm assemblies comprising various embodiments ofelectrodes may be employed. Examples of such clamp arm assemblies aredescribed in commonly-owned and contemporaneously-filed U.S. patentapplication Ser. Nos. 12/503,769, 12/503,770, and 12/503,766, each ofwhich is incorporated herein by reference in its entirety.

FIG. 13 is a schematic diagram of the tissue impedance module 502coupled to the blade 79 and the clamp arm assembly 415 with tissue 514located therebetween. With reference now to FIGS. 10-13, the generator500 comprises the tissue impedance module 502 configured for monitoringthe impedance of the tissue 514 (Z_(t)) located between the blade 79 andthe clamp arm assembly 451 during the tissue transection process. Thetissue impedance module 502 is coupled to the ultrasonic surgicalinstrument 120 by way of the cable 504. The cable 504 includes a first“energizing” conductor 504 a connected to the blade 79 (e.g., positive[+] electrode) and a second “return” conductor 504 b connected to theconductive jacket 472 (e.g., negative [−] electrode) of the clamp armassembly 451. In one embodiment, RF voltage v_(rf) is applied to theblade 79 to cause RF current i_(rf) to flow through the tissue 514. Thesecond conductor 504 b provides the return path for the current i_(rf)back to the tissue impedance module 502. The distal end of the returnconductor 504 b is connected to the conductive jacket 472 such that thecurrent i_(rf) can flow from the blade 79, through the tissue 514positioned intermediate the conductive jacket 472 and the blade 79, andthe conductive jacket 472 to the return conductor 504 b. The impedancemodule 502 connects in circuit, by way of the first and secondconductors 504 a, b. In one embodiment, the RF energy may be applied tothe blade 79 through the ultrasonic transducer 50 and the waveguide 80(FIG. 2). It is worthwhile noting that the RF energy applied to thetissue 514 for purposes of measuring the tissue impedance Z_(t) is a lowlevel subtherapeutic signal that does not contribute in a significantmanner, or at all, to the treatment of the tissue 514.

Having described operational details of various embodiments of thesurgical system 190, operations for the above surgical system 190 may befurther described with reference to FIGS. 10-13 in terms of a processfor cutting and coagulating a blood vessel employing a surgicalinstrument comprising the input device 406 and the tissue impedancemodule 502. Although a particular process is described in connectionwith the operational details, it can be appreciated that the processmerely provides an example of how the general functionality describedherein can be implemented by the surgical system 190. Further, the givenprocess does not necessarily have to be executed in the order presentedherein unless otherwise indicated. As previously discussed, the inputdevice 406 may be employed to program the step function output (e.g.,current, voltage, frequency) to the ultrasonic transducer 50/blade 79assembly.

In one embodiment, a first conductor or wire may be connected to theouter sheath 72 of the instrument 120 and a second conductor or wire maybe connected to the blade 79/transducer 50. By nature of the design, theblade 79 and the transducer 50 are electrically isolated from the outersheath 72 as well as other elements of the actuation mechanism for theinstrument 120 including the base 449 and the inner sheath 76. The outersheath 79 and other elements of the actuation mechanism including thebase 449 and the inner sheath 76 are all electrically continuous withone another—that is, they are all metallic and touch one another.Accordingly, by connecting a first conductor to the outer sheath 72 andconnecting a second conductor to the blade 79 or the transducer 50 suchthat the tissue resides between these two conductive pathways, thesystem can monitor the electrical impedance of the tissue as long as thetissue contacts both the blade 79 and the base 449. To facilitate thiscontact, the base 449 itself may include outwardly and possiblydownwardly protruding features to assure tissue contact while,effectively integrating conductive jacket 472 into base 449.

In one embodiment, the ultrasonic surgical instrument 120 may beoperated in accordance with a programmed step function algorithm 402responsive to the tissue impedance Z_(t). In one embodiment, a frequencystep function output may be initiated based on a comparison of thetissue impedance Z_(t) and predetermined thresholds that have beencorrelated with various tissue states (e.g., desiccation, transection,sealing). When the tissue impedance Z_(t) transitions above or below(e.g., crosses) a threshold, the processor 400 applies a digitalfrequency signal 418 to the DDS circuit 420 to change the frequency ofan ultrasonic oscillator by a predetermined step in accordance with thestep function algorithm 402 responsive to the tissue impedance Z_(t).

In operation, the blade 79 is located at the tissue treatment site. Thetissue 514 is grasped between the blade 79 and the clamp arm assembly451 such that the blade 79 and the conductive jacket 472 make electricalcontact with the tissue 514. The processor 400 applies a first digitalfrequency signal 418 to set a first drive frequency f₁ that is offresonance (e.g., f_(o)/2, 2f_(o) or other structural resonantfrequencies, where f_(o) is the resonant frequency). The blade 79 iselectrically energized by the low level subtherapeutic RF voltage v_(rf)supplied by the tissue impedance module 502. The drive signal 416 isapplied to the transducer 50/blade 79 in response to actuation of theswitch 312 a on the handle assembly 68 or the foot switch 434 until thetissue impedance Z_(t) changes by a predetermined amount. A force orload is then applied to the clamp arm assembly 451 and the blade 79.During this period the ultrasonic transducer 50 mechanically activatesthe blade 79 at the first drive frequency f₁ and as a result, the tissue514 begins to desiccate from the ultrasonic action applied between theblade 79 and the one or more clamp pads 58 of the clamp arm assembly 451causing the tissue impedance Z_(t) to increase. Eventually, as thetissue is transected by the ultrasonic action and applied clamp force,the tissue impedance Z_(t) becomes very high or infinite as the tissuefully transects such that no conductive path exists between the blade 79and the conductive jacket 472. It will be appreciated by those skilledin the art that the drive current (I) output also may be stepped asdescribed with reference to FIGS. 6-8 based on the tissue impedanceZ_(t).

In one embodiment, the tissue impedance Z_(t) may be monitored by theimpedance module 502 in accordance with the following process. Ameasurable RF current i1 is conveyed through the first energizingconductor 504 a to the blade 79, through the tissue 514, and back to theimpedance module 502 through the conductive jacket 472 and the secondconductor 504 b. As the tissue 514 is desiccated and cut by theultrasonic action of the blade 79 acting against the one or more clamppads 58, the impedance of the tissue 514 increases and thus the currenti1 in the return path, i.e., the second conductor 504 b, decreases. Theimpedance module 502 measures the tissue impedance Z_(t) and conveys arepresentative signal to the ADC 432 whose digital output 433 isprovided to the processor 400. The processor 400 calculates the tissueimpedance Z_(t) based on these measured values of v_(rf) and i_(rf). Theprocessor 400 steps the frequency by any suitable increment or decrementin response to changes in tissue impedance Z_(t). The processor 400controls the drive signals 416 and can make any necessary adjustments inamplitude and frequency in response to the tissue impedance Z_(t). Inone embodiment, the processor 400 can cut off the drive signal 416 whenthe tissue impedance Z_(t) reaches a predetermined threshold value.

Accordingly, by way of example, and not limitation, in one embodiment,the ultrasonic surgical instrument 120 may be operated in accordancewith a programmed stepped output algorithm to separate the inner musclelayer of a vessel from the adventitia layer prior to transecting andsealing the vessel. As previously discussed, according to one stepfunction algorithm, the processor 400 initially sets a first drivefrequency f1 that is significantly off resonance. The transducer 50 isactivated to separate the inner muscle layer of the vessel from theadventitia layer and the tissue impedance module 502 applies asubtherapeutic RF voltage v_(rf) signal to the blade 79. During thisperiod T₁ of operation the processor 400 monitors the tissue impedanceZ_(t) to determine when the inner muscle layer is transected orseparated from the adventitia layer. The tissue impedance Z_(t) iscorrelated to the load applied to the blade 79, for example, when thetissue becomes desiccated or when the tissue is transected the tissueimpedance Z_(t) becomes extremely high or infinite. The change in tissueimpedance Z_(t) indicates that the vessel has been separated ortransected from the inner muscle layer and the generator 500 isdeactivated for a second period of time T₂. The processor 400 then setsthe drive frequency to the resonant frequency f_(o). The vessel is thengrasped between the blade 79 and the clamp arm assembly 451 and thetransducer 50 is reactivated to transect and seal the vessel. Continuousmonitoring of the tissue impedance Z_(t) provides an indication of whenthe vessel is transected and sealed. Also, the tissue impedance Z_(t)may be monitored to provide an indication of the completeness of thetissue cutting and/or coagulating process or to stop the activation ofthe ultrasonic generator 500 when the tissue impedance Z_(t) reaches apredetermined threshold value. The threshold for the tissue impedanceZ_(t) may be selected, for example, to indicate that the vessel has beentransected. In one embodiment, the tissue impedance Z_(t) may rangebetween about 10 Ohms to about 1000 Ohms from an initial point to apoint just before the muscle layer is transected and sealed.

The applicants have discovered that experiments that run varying currentset points (both increasing and decreasing) and dwell times indicatethat the described embodiments can be used to separate the inner musclelayer from the outer adventitia layer prior to completing thetransection resulting in improved hemostasis and potentially lower totalenergy (heat) at the transection site. Furthermore, although thesurgical instruments 100, 120 have been described in regards toimpedance threshold detection schemes to determine when the muscle layeris separated from the adventitia, other embodiments that do not employany detection scheme are within the scope of the present disclosure. Forexample, embodiments of the surgical instruments 100, 120 may beemployed in simplified surgical systems wherein non-resonant power isapplied to separate the layers for a predetermined time of approximately1 second or less, prior to applying a resonant power to cut the tissue.The embodiments are not limited in this context.

Having described operational details of various embodiments of thesurgical systems 19 (FIG. 1) and 190 (FIG. 10), operations for the abovesurgical systems 19, 190 may be further described generally in terms ofa process for cutting and coagulating tissue employing a surgicalinstrument comprising the input device 406 and the tissue impedancemodule 502. Although a particular process is described in connectionwith the operational details, it can be appreciated that the processmerely provides an example of how the general functionality describedherein can be implemented by the surgical systems 19, 190. Further, thegiven process does not necessarily have to be executed in the orderpresented herein unless otherwise indicated. As previously discussed,the input device 406 may be employed to program the stepped output(e.g., current, frequency) to the ultrasonic transducer 50/blade 79assembly.

FIG. 14 illustrates one embodiment of a method 600 for driving an endeffector coupled to an ultrasonic drive system of a surgical instrument.With reference to FIGS. 1-3, and 6-14, by way of example, and notlimitation, the ultrasonic surgical instruments 100, 120 may be operatedin accordance with the method 600 to separate the inner muscle layer ofa vessel from the adventitia layer prior to transecting and sealing thevessel. Accordingly, in various embodiments, an end effector (e.g., endeffector 81, 810) of a surgical instrument (e.g., surgical instrument100, 120) may be driven in accordance with the method 600. A generator(e.g., generator 30, 500) is coupled to an ultrasonic drive system. Theultrasonic drive system comprises an ultrasonic transducer (e.g.,ultrasonic transducer 50) coupled to a waveguide (e.g., waveguide 80)and the end effector 81 is coupled to the waveguide 80. The ultrasonicdrive system is configured to resonate at a resonant frequency (e.g.,55.5 kHz). In one embodiment, at 602, the generator 30 generates a firstultrasonic drive signal. At 604, the ultrasonic transducer 50 isactuated with the first ultrasonic drive signal for a first period inresponse to activating a switch (e.g., switch 34) on a handle assembly(e.g., handle assembly 68) or a foot switch (e.g., foot switch 434)connected to the generator 30. After the first period, at 606, thegenerator 30 generates a second ultrasonic drive signal. At 608, theultrasonic transducer 50 is actuated with the second ultrasonic drivesignal for a second period in response to activating the switch 34 onthe handle assembly 68 or the foot switch 434 connected to the generator30. The first drive signal is different from the second drive signalover the respective first and second periods. The first and second drivesignals define a step function waveform over the first and secondperiods.

In one embodiment, the generator 30 generates a third ultrasonic drivesignal. The ultrasonic transducer 50 is actuated with the thirdultrasonic drive signal for a third period. The third drive signal isdifferent from the first second drive signals over the first, second,and third periods. The first, second, and third drive signals define astep function waveform over the first, second, and third periods. In oneembodiment, generating the first, second, and third ultrasonic drivesignals comprises generating a corresponding first, second, and thirddrive current and actuating the ultrasonic transducer 50 with the firstdrive current for the first period, actuating the ultrasonic transducer50 with the second drive current for the second period, and actuatingthe ultrasonic transducer 50 with the third drive current for the thirdperiod.

In one embodiment, the generator 30 generates the first ultrasonic drivesignal at a first frequency, which is different from the resonantfrequency. The ultrasonic transducer 50 is then actuated with the firstultrasonic drive signal at the first frequency for the first period.Actuation at the first frequency provides a first level of mechanicalvibration to the end effector 81 suitable for separating a first tissuefrom a second tissue, for example, to separate the inner muscle layer ofa vessel from the adventitia layer. The generator 30 generates thesecond ultrasonic drive signal at the resonant frequency, e.g., 55.5kHz, and the actuates the ultrasonic transducer 50 with the secondultrasonic drive signal at the resonant frequency for the second periodsubsequent to the first period. Actuation at the second, resonantfrequency, provides a second level of mechanical vibration to the endeffector 81 suitable for transecting and sealing the first tissue, suchas the vessel, once it separated from the inner muscle layer. In oneembodiment, the second ultrasonic drive signal at the resonant frequencyis generated automatically by the generator 30 after the first period.In one embodiment, the first frequency is substantially different fromthe resonant frequency and the first period is less than about onesecond. For example, in one embodiment, the first frequency is definedby the following equation: f₁=2*f_(o), wherein f₁ is the first frequencyand f_(o) is the resonant frequency. In another embodiment, the firstfrequency is defined by the following equation: f₁=f_(o)/2, wherein f₁is the first frequency and f_(o) is the resonant frequency. The first,second, and third ultrasonic drive signals are also envisioned to excitebe vibratory modes of the ultrasonic transducer 50 in longitudinal,flexural, and torsional modes and harmonics thereof.

In one embodiment, the generator 30 monitors a measurable characteristicof the ultrasonic drive system and generates any one of the first andsecond drive signals based on the measured characteristic. For example,the generator 30 monitors the impedance Z of the ultrasonic transducer50. The generator 30 comprises electronic circuitry suitable formeasuring the impedance of the transducer 50. For example, a currentsense circuit (e.g., current sense circuit 426) senses the currentflowing through the transducer 50 and a voltage sense circuit (e.g.,voltage sense circuit 428) senses the output voltage applied to thetransducer 50. A multiplexer (e.g., multiplexer 430) routes theappropriate analog signal to an analog-to-digital converter (e.g., ADC432), whose digital output is provided to a processor (e.g., processor400). The processor 400 calculates the transducer impedance Z based onthe measured values of current and voltage.

In one embodiment, the generator 500 comprises an impedance module(e.g., tissue impedance module 502) to measure the impedance of a tissueportion contacting an end effector (e.g., end effector 810). Theimpedance module 502 includes an RF oscillator (e.g., RF oscillator 506)to generate a subtherapeutic RF signal. The subtherapeutic RF signal isapplied to a blade (e.g., blade 79) portion of the end effector 810,which forms an energizing electrode. The tissue portion is graspedbetween the end effector 810 and a return electrode of a clamp armassembly (e.g., clamp arm assembly 451) and the impedance of the tissue(e.g., tissue 514). The tissue impedance is then measured by a voltagesense circuit (e.g., voltage sense circuit 508) and current sensecircuit (e.g., current sense circuit 510) and of the impedance module502. These signals are applied to the ADC 432 via the multiplexer 430.The digital output of the ADC 432 is provided to the processor 400,which calculates the tissue impedance Zt based on the measured values ofcurrent through the tissue and the voltage applied to the blade 79portion of the end effector 810.

FIGS. 15A-C illustrate various embodiments of logic flow diagrams of700, 800, 900 of operations for determining a change of state of tissuebeing manipulated by an ultrasonic surgical instrument and providingfeedback to the user to indicate that the tissue has undergone suchchange of state or that there is a high likelihood that the tissue hasundergone such change of state. As used herein, the tissue may undergo achange of state when the tissue is separated from other layers of tissueor bone, when the tissue is cut or transected, when the tissue iscoagulated, and so forth while being manipulated with an end effector ofan ultrasonic surgical instrument, such as, for example, the endeffector 81, 810 of the ultrasonic surgical instrument 100, 120 shown inFIGS. 1 and 10. A change in tissue state may be determined based on thelikelihood of an occurrence of a tissue separation event.

In various embodiments, the feedback is provided by the output indicator412 shown in FIGS. 9 and 11. The output indicator 412 is particularlyuseful in applications where the tissue being manipulated by the endeffector 81, 810 is out of the user's field of view and the user cannotsee when a change of state occurs in the tissue. The output indicator412 communicates to the user that a change in tissue state has occurredas determined in accordance with the operations described with respectto the logic flow diagrams 700, 800, 900. As previously discussed, theoutput indicator 412 may be configured to provide various types offeedback to the user including, without limitation, visual, audible,and/or tactile feedback to indicate to the user (e.g., surgeon,clinician) that the tissue has undergone a change of state or conditionof the tissue. By way of example, and not limitation, as previouslydiscussed, visual feedback comprises any type of visual indicationdevice including incandescent lamps or LEDs, graphical user interface,display, analog indicator, digital indicator, bar graph display, digitalalphanumeric display. By way of example, and not limitation, audiblefeedback comprises any type of buzzer, computer generated tone,computerized speech, VUI to interact with computers through avoice/speech platform. By way of example, and not limitation, tactilefeedback comprises any type of vibratory feedback provided through theinstrument housing handle assembly 68. The change of state of the tissuemay be determined based on transducer and tissue impedance measurementsas previously described, or based on voltage, current, and frequencymeasurements in accordance with the operations described with respect tothe logic flow diagrams 700, 800, 900 described below with respect toFIGS. 15A-C.

In one embodiment, the logic flow diagrams 700, 800, 900 may beimplemented as executable modules (e.g., algorithms) comprising computerreadable instructions to be executed by the processor 400 (FIGS. 9, 11,14) portion of the generator 30, 500. In various embodiments, theoperations described with respect to the logic flow diagrams 700, 800,900 may be implemented as one or more software components, e.g.,programs, subroutines, logic; one or more hardware components, e.g.,processors, DSPs, PLDs, ASICs, circuits, registers; and/or combinationsof software and hardware. In one embodiment, the executable instructionsto perform the operations described by the logic flow diagrams 700, 800,900 may be stored in memory. When executed, the instructions cause theprocessor 400 to determine a change in tissue state in accordance withthe operations described in the logic flow diagrams 800 and 900 andprovide feedback to the user by way of the output indicator 412. Inaccordance with such executable instructions, the processor 400 monitorsand evaluates the voltage, current, and/or frequency signal samplesavailable from the generator 30, 500 and according to the evaluation ofsuch signal samples determines whether a change in tissue state hasoccurred. As further described below, a change in tissue state may bedetermined based on the type of ultrasonic instrument and the powerlevel that the instrument is energized at. In response to the feedback,the operational mode of the ultrasonic surgical instrument 100, 120 maybe controlled by the user or may be automatically or semi-automaticallycontrolled.

FIG. 15A illustrates a logic flow diagram 700 of one embodiment ofdetermining a change in tissue state and activating the output indicator412 accordingly. With reference now to the logic flow diagram 700 shownin FIG. 15A and the drive system 32 of the generator 30 shown in FIG. 9,at 702, the processor 400 portion of the drive system 32 samples thevoltage (v), current (i), and frequency (f) signals of the generator 30.In the illustrated embodiment, at 704, the frequency and voltage signalsamples are analyzed separately to determine the corresponding frequencyinflection and/or voltage drop points. In other embodiments, the currentsignal samples may be separately analyzed in addition to the voltage andfrequency signal samples or in place of the voltage signal samples. At706, the present frequency signal sample is provided to a frequencyinflection point analysis module for determining a change in tissuestate as illustrated in the logic flow diagram 800 in FIG. 15B. At 708,the present voltage signal sample is provided to a voltage drop pointanalysis module for determining a change in tissue state as illustratedin the logic flow diagram 900 in FIG. 15C.

The frequency inflection point analysis module and the voltage droppoint analysis module determine when a change in tissue state hasoccurred based on correlated empirical data associated with a particularultrasonic instrument type and the energy level at which the instrumentis driven. At 714, the results 710 from the frequency inflection pointanalysis module and/or the results 712 from the voltage drop pointanalysis module are read by the processor 400. The processor 400determines 716 whether the frequency inflection point result 710 and/orthe voltage drop point result 712 indicates a change in tissue state. Ifthe results 710, 714 do not indicate a change in tissue state, theprocessor 400 continues along the “No” branch to 702 and reads anadditional voltage and frequency signal sample from the generator 30. Inembodiments that utilize the generator current in the analysis, theprocessor 400 would now also read an additional current signal samplefrom the generator 30. If the results 710, 714 indicate a sufficientchange in tissue state, the processor 400 continues along the “Yes”branch to 718 and activates the output indicator 412.

As previously discussed, the output indicator 412 may provide visual,audible, and/or tactile feedback to alert the user of the ultrasonicsurgical instrument 100, 120 that a change in tissue state has occurred.In various embodiments, in response to the feedback from the outputindicator 412, the operational mode of the generator 30, 500 and/or theultrasonic instrument 100, 120 may be controlled manually,automatically, or semi-automatically. The operational modes include,without limitation, disconnecting or shutting down the output power ofthe generator 30, 500, reducing the output power of the generator 30,500, cycling the output power of the generator 30, 500, pulsing theoutput power of the generator 30, 500, and/or outputting a high-powermomentary surge from the generator 30, 500. The operational modes of theultrasonic instrument in response to the change in tissue state can beselected, for example, to minimize heating effects of the end effector81, 810, e.g., of the clamp pad 58 (FIGS. 1-3), to prevent or minimizepossible damage to the surgical instrument 100, 120 and/or surroundingtissue. This is advantageous because heat is generated rapidly when thetransducer 50 is activated with nothing between the jaws of the endeffector 81, 810 as is the case when a change in tissue state occurssuch as when tissue has substantially separated from the end effector.

FIG. 15B is a logic flow diagram 800 illustrating one embodiment of theoperation of the frequency inflection point analysis module. At 802, afrequency sample is received by the processor 400 from 706 of the logicflow diagram 700. At 804, the processor 400 calculates an exponentiallyweighted moving average (EWMA) for the frequency inflection analysis.The EWMA is calculated to filter out noise from the generator from thefrequency samples. The EWMA is calculated in accordance with a frequencymoving average equation 806 and an alpha value (α) 808:

S _(tf) =αY _(tf)+(1−α)S _(tf)−1  (2)

Where:

S_(tf)=the current moving average of the sampled frequency signal;S_(tf-1)=the previous moving average of the sampled frequency signal;α=the smoothing factor; andY_(tf)=current data point of the sampled frequency signal.

The α value 808 may vary from about 0 to about 1 in accordance with adesired filtering or smoothing factor, wherein small α values 808approaching about 0 provide a large amount of filtering or smoothing andlarge α values 808 approaching about 1 provide a small amount offiltering or smoothing. The α value 808 may be selected based on theultrasonic instrument type and power level. In one embodiment, blocks804, 806, and 808 may be implemented as a variable digital low passfilter 810 with the α value 808 determining the cutoff point of thefilter 810. Once the frequency samples are filtered, the slope of thefrequency samples is calculated at 812 as:

Frequency Slope=Δf/Δt  (3)

The calculated Frequency Slope data points are provided to a “slowresponse” moving average filter 814 to calculate the EWMA moving averagefor the Frequency Slope to further reduce system noise. In oneembodiment, the “slow response” moving average filter 814 may beimplemented by calculating the EWMA for the Frequency Slope at 818 inaccordance with the frequency slope moving average equation 820 andalpha value (α′) 822:

S′ _(tf) =α′Y′ _(tf)+(1−α′)S′ _(tf-1)  (4)

Where:

S′_(tf)=the current moving average of the frequency slope of the sampledfrequency signal;S′_(tf-1)=the previous moving average of the frequency slope of thesampled frequency signal;α′=the smoothing factor; andY′_(tf)=current slope data point of the sampled frequency signal.

The α′ value 822 varies from about 0 to about 1, as previously discussedwith respect to digital filter block 810 in accordance with a desiredfiltering or smoothing factor, wherein small α′ value 822 approaching 0provide a large amount of filtering or smoothing and large α′ value 822approaching 1 provide a small amount of filtering or smoothing. The α′value 822 may be selected based on the ultrasonic instrument type andpower level.

The calculated Frequency Slope data points are provided to a “fastresponse” filter 816 to calculate the moving average for the FrequencySlope. At 824, the “fast response” filter 816 calculates the movingaverage for the Frequency Slope based on a number of data points 826.

In the illustrated embodiment, the output of the “slow response” movingaverage filter 814 “Slope EWMA” is applied to a (+) input of an adder828 and the output of the “fast response” filter 816 “Slope Avg” isapplied to (−) input of the adder 828. The adder 828 computes thedifference between the outputs of the “slow response” moving averagefilter 814 and the “fast response” filter 816. The difference betweenthese outputs is compared at 830 to a predetermined limit 832. The limit832 is determined based on the type of ultrasonic instrument and thepower level at which the particular type of ultrasonic instrument isenergized at. The limit 832 value may be predetermined and stored inmemory in the form of a look-up table or the like. If the differencebetween the “Slope EWMA” and the “Slope Avg” is not greater than thelimit 832, the processor 400 continues along the “No” branch and returnsa value 834 to the results 710 block that indicates that no inflectionpoint was found in the sampled frequency signal and, therefore, nochange in tissue state was detected. However, if the difference betweenthe “Slope EWMA” and the “Slope Avg” is greater than the limit 832, theprocessor 400 continues along the “Yes” branch and determines that afrequency inflection point 836 was found and returns point index 838 tothe results 710 block indicating that an inflection point was found inthe sampled frequency data and, therefore, a change in tissue state wasdetected. As previously discussed with reference to FIG. 15A, if afrequency inflection point 836 is found, then, at 718 (FIG. 15A) theprocessor 400 activates the change in tissue state indicator 718.

FIG. 15C is a logic flow diagram 900 illustrating one embodiment of theoperation of the voltage drop analysis module. At 902, a voltage sampleis received by the processor 400 from 708 of the logic flow diagram 700.At 904, the processor 400 calculates an exponentially weighted movingaverage (EWMA) for the frequency inflection analysis. The EWMA iscalculated to filter out noise from the generator from the frequencysamples. The EWMA is calculated in accordance with a voltage movingaverage equation 906 and an alpha value (α) 908:

S _(tv) =αY _(tv)+(1−α)S _(tv-1)  (5)

Where:

S_(tv)=the current moving average of the sampled voltage signal;S_(tv-1)=the previous moving average of the sampled voltage signal;α=the smoothing factor; andY_(tv)=current data point of the sampled voltage signal.

As previously discussed, the α value 908 may vary from 0 to 1 inaccordance with a desired filtering or smoothing factor and may beselected based on the ultrasonic instrument type and power level. In oneembodiment, blocks 904, 906, and 908 may be implemented as a variabledigital low pass filter 910 with the α value 908 determining the cutoffpoint of the filter 910. Once the voltage samples are filtered, theslope of the voltage samples is calculated at 912 as:

Voltage Slope=Δv/Δt  (6)

The calculated Voltage Slope data points are provided to a “slowresponse” moving average filter 914 to calculate the EWMA moving averagefor the Voltage Slope to further reduce system noise. In one embodiment,the “slow response” moving average filter 914 may be implemented bycalculating the EWMA for the Voltage Slope at 918 in accordance with thevoltage slope moving average equation 920 and alpha value (α′) 822:

S′ _(tv) =α′Y′ _(tv)+(1−α′)S′ _(tv-1)  (7)

Where:

S′_(tv)=the current moving average of the voltage slope of the sampledvoltage signal;S′_(tv-1)=the previous moving average of the voltage slope of thesampled voltage signal;α′=the smoothing factor; andY′_(tv)=current slope data point of the sampled voltage signal.

The α′ value 922 varies from about 0 to about 1, as previously discussedwith respect to digital filter block 910 in accordance with a desiredfiltering or smoothing factor, wherein small α′ value 922 approachingabout 0 provide a large amount of filtering or smoothing and large α′value 922 approaching about 1 provide a small amount of filtering orsmoothing. The α′ value 922 may be selected based on the ultrasonicinstrument type and power level.

The calculated Voltage Slope data points are provided to a “fastresponse” filter 916 to calculate the moving average for the VoltageSlope. At 924, the “fast response” filter 916 calculates the movingaverage for the Voltage Slope based on a number of data points 926.

In the illustrated embodiment, the output of the “slow response” movingaverage filter 914 “Slope EWMA” is applied to a (+) input of an adder928 and the output of the “fast response” filter 916 “Slope Avg” isapplied to (−) input of the adder 928. The adder 928 computes thedifference between the outputs of the “slow response” moving averagefilter 914 and the “fast response” filter 916. The difference betweenthese outputs is compared at 930 to a predetermined limit 932. The limit932 is determined based on the type of ultrasonic instrument and thepower level at which the particular type of ultrasonic instrument isenergized at. The limit 932 value may be predetermined and stored inmemory in the form of a look-up table or the like. If the differencebetween the “Slope EWMA” and the “Slope Avg” is not greater than thelimit 932, the processor 400 continues along the “No” branch and resetsa counter to zero at 940, then returns a value 934 to the results 710block that indicates that no voltage drop point was found in the sampledvoltage signals and, therefore, no change in tissue state was detected.However, if the difference between the “Slope EWMA” and the “Slope Avg”is greater than the limit 932, the processor 400 continues along the“Yes” branch and increments a counter at 942. At 944, the processor 400decides whether the counter is greater than 1, or some otherpredetermined threshold value for example. In other words, the processor400 takes at least two data points in regards to the voltage drop point.If the counter is not greater than the threshold (e.g., 1 in theillustrated embodiment) the processor 400 continues along the “No”branch and returns a value 934 to the results 710 block that indicatesthat no voltage drop point was found in the sampled voltage signals and,therefore, no change in tissue state was detected. If the counter isgreater than the threshold (e.g., 1 in the illustrated embodiment) theprocessor 400 continues along the “Yes” branch and determines that avoltage drop point 936 was found and returns a point index 938 to theresults 712 block indicating that a voltage drop point was found in thesampled voltage signals and, therefore, a change in tissue state wasdetected. As previously discussed with reference to FIG. 15A, if avoltage point 836 is found, then, at 718 (FIG. 15A) the processor 400activates the change in tissue state indicator 718.

FIG. 16 illustrates one embodiment of a surgical system 1000 comprisinga generator 1002 and various surgical instruments usable therewith. Thegenerator 1002 is configurable for use with surgical devices. Accordingto various embodiments, the generator 1002 may be configurable for usewith different surgical devices of different types including, forexample, the ultrasonic device 1004 and electrosurgical or RF surgicaldevices, such as, the RF device 1006. Although in the embodiment of FIG.16, the generator 1002 is shown separate from the surgical devices 1004,1006, in one embodiment, the generator 1002 may be formed integrallywith either of the surgical devices 1004, 1006 to form a unitarysurgical system. The generator 1002 comprises an input device 1009located on a front panel of the generator 1002 console. The input device1009 may comprise any suitable device that generates signals suitablefor programming the operation of the generator 1002.

FIG. 17 is a diagram of the surgical system 1000 of FIG. 16. In variousembodiments, the generator 1002 may comprise several separate functionalelements, such as modules and/or blocks. Different functional elementsor modules may be configured for driving the different kinds of surgicaldevices 1004, 1006. For example, an ultrasonic generator module 1008 maydrive ultrasonic devices such as the ultrasonic device 1004. Anelectrosurgery/RF generator module 1010 may drive the electrosurgicaldevice 1006. For example, the respective modules 1008, 1010 may generaterespective drive signals for driving the surgical devices 1004, 1006. Invarious embodiments, the ultrasonic generator module 1008 and/or theelectrosurgery/RF generator module 1010 each may be formed integrallywith the generator 1002. Alternatively, one or more of the modules 1008,1010 may be provided as a separate circuit module electrically coupledto the generator 1002. (The modules 1008 and 1010 are shown in phantomto illustrate this option.) Also, in some embodiments, theelectrosurgery/RF generator module 1010 may be formed integrally withthe ultrasonic generator module 1008, or vice versa.

In accordance with the described embodiments, the ultrasonic generatormodule 1008 may produce a drive signal or signals of particularvoltages, currents, and frequencies, e.g., 55,500 cycles per second(Hz). The drive signal or signals may be provided to the ultrasonicdevice 1004, and specifically to the transducer 1014, which may operate,for example, as described above. In one embodiment, the generator 1002may be configured to produce a drive signal of a particular voltage,current, and/or frequency output signal that can be stepped with highresolution, accuracy, and repeatability.

The generator 1002 may be activated to provide the drive signal to thetransducer 1014 in any suitable manner. For example, the generator 1002may comprise a foot switch 1020 coupled to the generator 1002 via afootswitch cable 1022. A clinician may activate the transducer 1014 bydepressing the foot switch 1020. In addition, or instead of the footswitch 1020 some embodiments of the ultrasonic device 1004 may utilizeone or more switches positioned on the hand piece that, when activated,may cause the generator 1002 to activate the transducer 1014. In oneembodiment, for example, the one or more switches may comprise a pair oftoggle buttons 1036 a, 1036 b (FIG. 16), for example, to determine anoperating mode of the device 1004. When the toggle button 1036 a isdepressed, for example, the ultrasonic generator 1002 may provide amaximum drive signal to the transducer 1014, causing it to producemaximum ultrasonic energy output. Depressing toggle button 1036 b maycause the ultrasonic generator 1002 to provide a user-selectable drivesignal to the transducer 1014, causing it to produce less than themaximum ultrasonic energy output. The device 1004 additionally oralternatively may comprise a second switch (not shown) to, for example,indicate a position of a jaw closure trigger for operating jaws of theend effector 1026. Also, in some embodiments, the ultrasonic generator1002 may be activated based on the position of the jaw closure trigger,(e.g., as the clinician depresses the jaw closure trigger to close thejaws, ultrasonic energy may be applied).

Additionally or alternatively, the one or more switches may comprises atoggle button 1036 c that, when depressed, causes the generator 1002 toprovide a pulsed output. The pulses may be provided at any suitablefrequency and grouping, for example. In certain embodiments, the powerlevel of the pulses may be the power levels associated with togglebuttons 1036 a, 1036 b (maximum, less than maximum), for example.

It will be appreciated that a device 1004 may comprise any combinationof the toggle buttons 1036 a, 1036 b, 1036 c. For example, the device1004 could be configured to have only two toggle buttons: a togglebutton 1036 a for producing maximum ultrasonic energy output and atoggle button 1036 c for producing a pulsed output at either the maximumor less than maximum power level. In this way, the drive signal outputconfiguration of the generator 1002 could be 5 continuous signals and 5or 4 or 3 or 2 or 1 pulsed signals. In certain embodiments, the specificdrive signal configuration may be controlled based upon, for example,EEPROM settings in the generator 1002 and/or user power levelselection(s).

In certain embodiments, a two-position switch may be provided as analternative to a toggle button 1036 c. For example, a device 1004 mayinclude a toggle button 1036 a for producing a continuous output at amaximum power level and a two-position toggle button 1036 b. In a firstdetented position, toggle button 1036 b may produce a continuous outputat a less than maximum power level, and in a second detented positionthe toggle button 1036 b may produce a pulsed output (e.g., at either amaximum or less than maximum power level, depending upon the EEPROMsettings).

In accordance with the described embodiments, the electrosurgery/RFgenerator module 1010 may generate a drive signal or signals with outputpower sufficient to perform bipolar electrosurgery using radio frequency(RF) energy. In bipolar electrosurgery applications, the drive signalmay be provided, for example, to electrodes of the electrosurgicaldevice 1006, for example. Accordingly, the generator 1002 may beconfigured for therapeutic purposes by applying electrical energy to thetissue sufficient for treating the tissue (e.g., coagulation,cauterization, tissue welding).

The generator 1002 may comprise an input device 1045 (FIG. 16) located,for example, on a front panel of the generator 1002 console. The inputdevice 1045 may comprise any suitable device that generates signalssuitable for programming the operation of the generator 1002. Inoperation, the user can program or otherwise control operation of thegenerator 1002 using the input device 1045. The input device 1045 maycomprise any suitable device that generates signals that can be used bythe generator (e.g., by one or more processors contained in thegenerator) to control the operation of the generator 1002 (e.g.,operation of the ultrasonic generator module 1008 and/orelectrosurgery/RF generator module 1010). In various embodiments, theinput device 1045 includes one or more of buttons, switches,thumbwheels, keyboard, keypad, touch screen monitor, pointing device,remote connection to a general purpose or dedicated computer. In otherembodiments, the input device 1045 may comprise a suitable userinterface, such as one or more user interface screens displayed on atouch screen monitor, for example. Accordingly, by way of the inputdevice 1045, the user can set or program various operating parameters ofthe generator, such as, for example, current (I), voltage (V), frequency(f), and/or period (T) of a drive signal or signals generated by theultrasonic generator module 1008 and/or electrosurgery/RF generatormodule 1010.

The generator 1002 may also comprise an output device 1047 (FIG. 16),such as an output indicator, located, for example, on a front panel ofthe generator 1002 console. The output device 1047 includes one or moredevices for providing a sensory feedback to a user. Such devices maycomprise, for example, visual feedback devices (e.g., a visual feedbackdevice may comprise incandescent lamps, light emitting diodes (LEDs),graphical user interface, display, analog indicator, digital indicator,bar graph display, digital alphanumeric display, LCD display screen, LEDindicators), audio feedback devices (e.g., an audio feedback device maycomprise speaker, buzzer, audible, computer generated tone, computerizedspeech, voice user interface (VUI) to interact with computers through avoice/speech platform), or tactile feedback devices (e.g., a tactilefeedback device comprises any type of vibratory feedback, hapticactuator).

Although certain modules and/or blocks of the generator 1002 may bedescribed by way of example, it can be appreciated that a greater orlesser number of modules and/or blocks may be used and still fall withinthe scope of the embodiments. Further, although various embodiments maybe described in terms of modules and/or blocks to facilitatedescription, such modules and/or blocks may be implemented by one ormore hardware components, e.g., processors, Digital Signal Processors(DSPs), Programmable Logic Devices (PLDs), Application SpecificIntegrated Circuits (ASICs), circuits, registers and/or softwarecomponents, e.g., programs, subroutines, logic and/or combinations ofhardware and software components.

In one embodiment, the ultrasonic generator drive module 1008 andelectrosurgery/RF drive module 1010 may comprise one or more embeddedapplications implemented as firmware, software, hardware, or anycombination thereof. The modules 1008, 1010 may comprise variousexecutable modules such as software, programs, data, drivers,application program interfaces (APIs), and so forth. The firmware may bestored in nonvolatile memory (NVM), such as in bit-masked read-onlymemory (ROM) or flash memory. In various implementations, storing thefirmware in ROM may preserve flash memory. The NVM may comprise othertypes of memory including, for example, programmable ROM (PROM),erasable programmable ROM (EPROM), electrically erasable programmableROM (EEPROM), or battery backed random-access memory (RAM) such asdynamic RAM (DRAM), Double-Data-Rate DRAM (DDRAM), and/or synchronousDRAM (SDRAM).

In one embodiment, the modules 1008, 1010 comprise a hardware componentimplemented as a processor for executing program instructions formonitoring various measurable characteristics of the devices 1004, 1006and generating a corresponding output control signals for operating thedevices 1004, 1006. In embodiments in which the generator 1002 is usedin conjunction with the device 1004, the output control signal may drivethe ultrasonic transducer 1014 in cutting and/or coagulation operatingmodes. Electrical characteristics of the device 1004 and/or tissue maybe measured and used to control operational aspects of the generator1002 and/or provided as feedback to the user. In embodiments in whichthe generator 1002 is used in conjunction with the device 1006, theoutput control signal may supply electrical energy (e.g., RF energy) tothe end effector 1032 in cutting, coagulation and/or desiccation modes.Electrical characteristics of the device 1006 and/or tissue may bemeasured and used to control operational aspects of the generator 1002and/or provide feedback to the user. In various embodiments, aspreviously discussed, the hardware component may be implemented as aDSP, PLD, ASIC, circuits, and/or registers. In one embodiment, theprocessor may be configured to store and execute computer softwareprogram instructions to generate the step function output signals fordriving various components of the devices 1004, 1006, such as theultrasonic transducer 1014 and the end effectors 1026, 1032.

FIG. 18 illustrates an equivalent circuit 1050 of an ultrasonictransducer, such as the ultrasonic transducer 1014, according to oneembodiment. The circuit 1050 comprises a first “motional” branch havinga serially connected inductance L_(s), resistance R_(s) and capacitanceC_(s) that define the electromechanical properties of the resonator, anda second capacitive branch having a static capacitance C_(o). Drivecurrent I_(g) may be received from a generator at a drive voltage V_(g),with motional current I_(m) flowing through the first branch and currentI_(g)-I_(m) flowing through the capacitive branch. Control of theelectromechanical properties of the ultrasonic transducer may beachieved by suitably controlling I_(g) and V_(g). As explained above,conventional generator architectures may include a tuning inductor L_(t)(shown in phantom in FIG. 18) for tuning out in a parallel resonancecircuit the static capacitance Co at a resonant frequency so thatsubstantially all of generator's current output I_(g) flows through themotional branch. In this way, control of the motional branch currentI_(m) is achieved by controlling the generator current output I_(g). Thetuning inductor L_(t) is specific to the static capacitance C_(o) of anultrasonic transducer, however, and a different ultrasonic transducerhaving a different static capacitance requires a different tuninginductor L_(t). Moreover, because the tuning inductor L_(t) is matchedto the nominal value of the static capacitance Co at a single resonantfrequency, accurate control of the motional branch current I_(m) isassured only at that frequency, and as frequency shifts down withtransducer temperature, accurate control of the motional branch currentis compromised.

Embodiments of the generator 1002 do not rely on a tuning inductor L_(t)to monitor the motional branch current I_(m). Instead, the generator1002 may use the measured value of the static capacitance C_(o) inbetween applications of power for a specific ultrasonic surgical device1004 (along with drive signal voltage and current feedback data) todetermine values of the motional branch current I_(m) on a dynamic andongoing basis (e.g., in real-time). Such embodiments of the generator1002 are therefore able to provide virtual tuning to simulate a systemthat is tuned or resonant with any value of static capacitance C_(o) atany frequency, and not just at single resonant frequency dictated by anominal value of the static capacitance C_(o).

FIG. 19 is a simplified block diagram of one embodiment of the generator1002 for proving inductorless tuning as described above, among otherbenefits. Additional details of the generator 1002 are described incommonly assigned and contemporaneously filed U.S. patent applicationSer. No. 12/896,360, now U.S. Patent Application Publication No.2011/0087256 A1, titled “Surgical Generator For Ultrasonic AndElectrosurgical Devices,” the disclosure of which is incorporated hereinby reference in its entirety. With reference to FIG. 19, the generator1002 may comprise a patient isolated stage 1052 in communication with anon-isolated stage 1054 via a power transformer 1056. A secondarywinding 1058 of the power transformer 1056 is contained in the isolatedstage 1052 and may comprise a tapped configuration (e.g., acenter-tapped or a non-center-tapped configuration) to define drivesignal outputs 1060 a, 1060 b, 1060 c for outputting drive signals todifferent surgical devices, such as, for example, an ultrasonic surgicaldevice 1004 and an electrosurgical device 1006. In particular, drivesignal outputs 1060 a, 1060 c may output a drive signal (e.g., a 420VRMS drive signal) to an ultrasonic surgical device 1004, and drivesignal outputs 1060 b, 160 c may output a drive signal (e.g., a 100V RMSdrive signal) to an electrosurgical device 1006, with output 1060 bcorresponding to the center tap of the power transformer 1056. Thenon-isolated stage 1054 may comprise a power amplifier 1062 having anoutput connected to a primary winding 1064 of the power transformer1056. In certain embodiments the power amplifier 1062 may be comprise apush-pull amplifier. For example, the non-isolated stage 1054 mayfurther comprise a logic device 1066 for supplying a digital output to adigital-to-analog converter (DAC) 1068, which in turn supplies acorresponding analog signal to an input of the power amplifier 1062. Incertain embodiments the logic device 1066 may comprise a programmablegate array (PGA), a field-programmable gate array (FPGA), programmablelogic device (PLD), among other logic circuits, for example. The logicdevice 1066, by virtue of controlling the input of the power amplifier1062 via the DAC 1068, may therefore control any of a number ofparameters (e.g., frequency, waveform shape, waveform amplitude) ofdrive signals appearing at the drive signal outputs 1060 a, 1060 b, 1060c. In certain embodiments and as discussed below, the logic device 1066,in conjunction with a processor (e.g., a digital signal processordiscussed below), may implement a number of digital signal processing(DSP)-based and/or other control algorithms to control parameters of thedrive signals output by the generator 1002.

Power may be supplied to a power rail of the power amplifier 1062 by aswitch-mode regulator 1070. In certain embodiments the switch-moderegulator 1070 may comprise an adjustable buck regulator, for example.The non-isolated stage 1054 may further comprise a first processor 1074,which in one embodiment may comprise a DSP processor such as an AnalogDevices ADSP-21469 SHARC DSP, available from Analog Devices, Norwood,Mass., for example, although in various embodiments any suitableprocessor may be employed. In certain embodiments the processor 1074 maycontrol operation of the switch-mode power converter 1070 responsive tovoltage feedback data received from the power amplifier 1062 by the DSPprocessor 1074 via an analog-to-digital converter (ADC) 1076. In oneembodiment, for example, the DSP processor 1074 may receive as input,via the ADC 1076, the waveform envelope of a signal (e.g., an RF signal)being amplified by the power amplifier 1062. The DSP processor 1074 maythen control the switch-mode regulator 1070 (e.g., via a pulse-widthmodulated (PWM) output) such that the rail voltage supplied to the poweramplifier 1062 tracks the waveform envelope of the amplified signal. Bydynamically modulating the rail voltage of the power amplifier 1062based on the waveform envelope, the efficiency of the power amplifier1062 may be significantly improved relative to a fixed rail voltageamplifier schemes.

In certain embodiments, the logic device 1066, in conjunction with theDSP processor 1074, may implement a direct digital synthesizer (DDS)control scheme to control the waveform shape, frequency and/or amplitudeof drive signals output by the generator 1002. In one embodiment, forexample, the logic device 1066 may implement a DDS control algorithm byrecalling waveform samples stored in a dynamically-updated look-up table(LUT), such as a RAM LUT, which may be embedded in an FPGA. This controlalgorithm is particularly useful for ultrasonic applications in which anultrasonic transducer, such as the ultrasonic transducer 1014, may bedriven by a clean sinusoidal current at its resonant frequency. Becauseother frequencies may excite parasitic resonances, minimizing orreducing the total distortion of the motional branch current maycorrespondingly minimize or reduce undesirable resonance effects.Because the waveform shape of a drive signal output by the generator1002 is impacted by various sources of distortion present in the outputdrive circuit (e.g., the power transformer 1056, the power amplifier1062), voltage and current feedback data based on the drive signal maybe input into an algorithm, such as an error control algorithmimplemented by the DSP processor 1074, which compensates for distortionby suitably pre-distorting or modifying the waveform samples stored inthe LUT on a dynamic, ongoing basis (e.g., in real-time). In oneembodiment, the amount or degree of pre-distortion applied to the LUTsamples may be based on the error between a computed motional branchcurrent and a desired current waveform shape, with the error beingdetermined on a sample-by-sample basis. In this way, the pre-distortedLUT samples, when processed through the drive circuit, may result in amotional branch drive signal having the desired waveform shape (e.g.,sinusoidal) for optimally driving the ultrasonic transducer. In suchembodiments, the LUT waveform samples will therefore not represent thedesired waveform shape of the drive signal, but rather the waveformshape that is required to ultimately produce the desired waveform shapeof the motional branch drive signal when distortion effects are takeninto account.

The non-isolated stage 1054 may further comprise an ADC 1078 and an ADC1080 coupled to the output of the power transformer 1056 via respectiveisolation transformers 1082, 1084 for respectively sampling the voltageand current of drive signals output by the generator 1002. In certainembodiments, the ADCs 1078, 1080 may be configured to sample at highspeeds (e.g., 80 MSPS) to enable oversampling of the drive signals. Inone embodiment, for example, the sampling speed of the ADCs 1078, 1080may enable approximately 200× (depending on frequency) oversampling ofthe drive signals. In certain embodiments, the sampling operations ofthe ADC 1078, 1080 may be performed by a singe ADC receiving inputvoltage and current signals via a two-way multiplexer. The use ofhigh-speed sampling in embodiments of the generator 1002 may enable,among other things, calculation of the complex current flowing throughthe motional branch (which may be used in certain embodiments toimplement DDS-based waveform shape control described above), accuratedigital filtering of the sampled signals, and calculation of real powerconsumption with a high degree of precision. Voltage and currentfeedback data output by the ADCs 1078, 1080 may be received andprocessed (e.g., FIFO buffering, multiplexing) by the logic device 1066and stored in data memory for subsequent retrieval by, for example, theDSP processor 1074. As noted above, voltage and current feedback datamay be used as input to an algorithm for pre-distorting or modifying LUTwaveform samples on a dynamic and ongoing basis. In certain embodiments,this may require each stored voltage and current feedback data pair tobe indexed based on, or otherwise associated with, a corresponding LUTsample that was output by the logic device 1066 when the voltage andcurrent feedback data pair was acquired. Synchronization of the LUTsamples and the voltage and current feedback data in this mannercontributes to the correct timing and stability of the pre-distortionalgorithm.

In certain embodiments, the voltage and current feedback data may beused to control the frequency and/or amplitude (e.g., current amplitude)of the drive signals. In one embodiment, for example, voltage andcurrent feedback data may be used to determine impedance phase. Thefrequency of the drive signal may then be controlled to minimize orreduce the difference between the determined impedance phase and animpedance phase setpoint (e.g., 0°), thereby minimizing or reducing theeffects of harmonic distortion and correspondingly enhancing impedancephase measurement accuracy. The determination of phase impedance and afrequency control signal may be implemented in the DSP processor 1074,for example, with the frequency control signal being supplied as inputto a DDS control algorithm implemented by the logic device 1066.

In another embodiment, for example, the current feedback data may bemonitored in order to maintain the current amplitude of the drive signalat a current amplitude setpoint. The current amplitude setpoint may bespecified directly or determined indirectly based on specified voltageamplitude and power setpoints. In certain embodiments, control of thecurrent amplitude may be implemented by control algorithm, such as, forexample, a PID control algorithm, in the processor 1074. Variablescontrolled by the control algorithm to suitably control the currentamplitude of the drive signal may include, for example, the scaling ofthe LUT waveform samples stored in the logic device 1066 and/or thefull-scale output voltage of the DAC 1068 (which supplies the input tothe power amplifier 1062) via a DAC 1086.

The non-isolated stage 1054 may further comprise a second processor 1090for providing, among other things user interface (UI) functionality. Inone embodiment, the UI processor 1090 may comprise an Atmel AT91SAM9263processor having an ARM 926EJ-S core, available from Atmel Corporation,San Jose, Calif., for example. Examples of UI functionality supported bythe UI processor 1090 may include audible and visual user feedback,communication with peripheral devices (e.g., via a Universal Serial Bus(USB) interface), communication with the footswitch 1020, communicationwith an input device 1009 (e.g., a touch screen display) andcommunication with an output device 1047 (e.g., a speaker). The UIprocessor 1090 may communicate with the processor 1074 and the logicdevice 1066 (e.g., via serial peripheral interface (SPI) buses).Although the UI processor 1090 may primarily support UI functionality,it may also coordinate with the DSP processor 1074 to implement hazardmitigation in certain embodiments. For example, the UI processor 1090may be programmed to monitor various aspects of user input and/or otherinputs (e.g., touch screen inputs, footswitch 1020 inputs (FIG. 17),temperature sensor inputs) and may disable the drive output of thegenerator 1002 when an erroneous condition is detected.

In certain embodiments, both the DSP processor 1074 and the UI processor1090, for example, may determine and monitor the operating state of thegenerator 1002. For the DSP processor 1074, the operating state of thegenerator 1002 may dictate, for example, which control and/or diagnosticprocesses are implemented by the DSP processor 1074. For the UIprocessor 1090, the operating state of the generator 1002 may dictate,for example, which elements of a user interface (e.g., display screens,sounds) are presented to a user. The respective DSP and UI processors1074, 1090 may independently maintain the current operating state of thegenerator 1002 and recognize and evaluate possible transitions out ofthe current operating state. The DSP processor 1074 may function as themaster in this relationship and determine when transitions betweenoperating states are to occur. The UI processor 1090 may be aware ofvalid transitions between operating states and may confirm if aparticular transition is appropriate. For example, when the DSPprocessor 1074 instructs the UI processor 1090 to transition to aspecific state, the UI processor 1090 may verify that requestedtransition is valid. In the event that a requested transition betweenstates is determined to be invalid by the UI processor 1090, the UIprocessor 1090 may cause the generator 1002 to enter a failure mode.

The non-isolated stage 1054 may further comprise a controller 1096 formonitoring input devices 1045 (e.g., a capacitive touch sensor used forturning the generator 1002 on and off, a capacitive touch screen). Incertain embodiments, the controller 1096 may comprise at least oneprocessor and/or other controller device in communication with the UIprocessor 1090. In one embodiment, for example, the controller 1096 maycomprise a processor (e.g., a Mega168 8-bit controller available fromAtmel) configured to monitor user input provided via one or morecapacitive touch sensors. In one embodiment, the controller 1096 maycomprise a touch screen controller (e.g., a QT5480 touch screencontroller available from Atmel) to control and manage the acquisitionof touch data from a capacitive touch screen.

In certain embodiments, when the generator 1002 is in a “power off”state, the controller 1096 may continue to receive operating power(e.g., via a line from a power supply of the generator 1002, such as thepower supply 2011 discussed below). In this way, the controller 196 maycontinue to monitor an input device 1045 (e.g., a capacitive touchsensor located on a front panel of the generator 1002) for turning thegenerator 1002 on and off. When the generator 1002 is in the power offstate, the controller 1096 may wake the power supply (e.g., enableoperation of one or more DC/DC voltage converters 2013 of the powersupply 2011) if activation of the “on/off” input device 1045 by a useris detected. The controller 1096 may therefore initiate a sequence fortransitioning the generator 1002 to a “power on” state. Conversely, thecontroller 1096 may initiate a sequence for transitioning the generator1002 to the power off state if activation of the “on/off” input device1045 is detected when the generator 1002 is in the power on state. Incertain embodiments, for example, the controller 1096 may reportactivation of the “on/off” input device 1045 to the processor 1090,which in turn implements the necessary process sequence fortransitioning the generator 1002 to the power off state. In suchembodiments, the controller 196 may have no independent ability forcausing the removal of power from the generator 1002 after its power onstate has been established.

In certain embodiments, the controller 1096 may cause the generator 1002to provide audible or other sensory feedback for alerting the user thata power on or power off sequence has been initiated. Such an alert maybe provided at the beginning of a power on or power off sequence andprior to the commencement of other processes associated with thesequence.

In certain embodiments, the isolated stage 1052 may comprise aninstrument interface circuit 1098 to, for example, provide acommunication interface between a control circuit of a surgical device(e.g., a control circuit comprising handpiece switches) and componentsof the non-isolated stage 1054, such as, for example, the programmablelogic device 1066, the DSP processor 1074 and/or the UI processor 190.The instrument interface circuit 1098 may exchange information withcomponents of the non-isolated stage 1054 via a communication link thatmaintains a suitable degree of electrical isolation between the stages1052, 1054, such as, for example, an infrared (IR)-based communicationlink. Power may be supplied to the instrument interface circuit 1098using, for example, a low-dropout voltage regulator powered by anisolation transformer driven from the non-isolated stage 1054.

In one embodiment, the instrument interface circuit 198 may comprise alogic device 2000 (e.g., logic circuit, programmable logic circuit, PGA,FPGA, PLD) in communication with a signal conditioning circuit 2002. Thesignal conditioning circuit 2002 may be configured to receive a periodicsignal from the logic circuit 2000 (e.g., a 2 kHz square wave) togenerate a bipolar interrogation signal having an identical frequency.The interrogation signal may be generated, for example, using a bipolarcurrent source fed by a differential amplifier. The interrogation signalmay be communicated to a surgical device control circuit (e.g., by usinga conductive pair in a cable that connects the generator 102 to thesurgical device) and monitored to determine a state or configuration ofthe control circuit. The control circuit may comprise a number ofswitches, resistors and/or diodes to modify one or more characteristics(e.g., amplitude, rectification) of the interrogation signal such that astate or configuration of the control circuit is uniquely discernablebased on the one or more characteristics. In one embodiment, forexample, the signal conditioning circuit 2002 may comprises an ADC forgenerating samples of a voltage signal appearing across inputs of thecontrol circuit resulting from passage of interrogation signaltherethrough. The logic device 2000 (or a component of the non-isolatedstage 1054) may then determine the state or configuration of the controlcircuit based on the ADC samples.

In one embodiment, the instrument interface circuit 1098 may comprise afirst data circuit interface 2004 to enable information exchange betweenthe logic circuit 2000 (or other element of the instrument interfacecircuit 1098) and a first data circuit disposed in or otherwiseassociated with a surgical device. In certain embodiments, for example,a first data circuit 2006 may be disposed in a cable integrally attachedto a surgical device handpiece, or in an adaptor for interfacing aspecific surgical device type or model with the generator 1002. Incertain embodiments, the first data circuit may comprise a non-volatilestorage device, such as an electrically erasable programmable read-onlymemory (EEPROM) device. In certain embodiments and referring again toFIG. 19, the first data circuit interface 2004 may be implementedseparately from the logic device 2000 and comprise suitable circuitry(e.g., discrete logic devices, a processor) to enable communicationbetween the programmable logic device 2000 and the first data circuit.In other embodiments, the first data circuit interface 2004 may beintegral with the logic device 2000.

In certain embodiments, the first data circuit 2006 may storeinformation pertaining to the particular surgical device with which itis associated. Such information may include, for example, a modelnumber, a serial number, a number of operations in which the surgicaldevice has been used, and/or any other type of information. Thisinformation may be read by the instrument interface circuit 1098 (e.g.,by the logic device 2000), transferred to a component of thenon-isolated stage 1054 (e.g., to logic device 1066, DSP processor 1074and/or UI processor 1090) for presentation to a user via an outputdevice 1047 and/or for controlling a function or operation of thegenerator 1002. Additionally, any type of information may becommunicated to first data circuit 2006 for storage therein via thefirst data circuit interface 2004 (e.g., using the logic device 2000).Such information may comprise, for example, an updated number ofoperations in which the surgical device has been used and/or datesand/or times of its usage.

As discussed previously, a surgical instrument may be detachable from ahandpiece (e.g., instrument 1024 may be detachable from handpiece 1016)to promote instrument interchangeability and/or disposability. In suchcases, conventional generators may be limited in their ability torecognize particular instrument configurations being used and tooptimize control and diagnostic processes accordingly. The addition ofreadable data circuits to surgical device instruments to address thisissue is problematic from a compatibility standpoint, however. Forexample, designing a surgical device to remain backwardly compatiblewith generators that lack the requisite data reading functionality maybe impractical due to, for example, differing signal schemes, designcomplexity, and cost. Embodiments of instruments discussed hereinaddress these concerns by using data circuits that may be implemented inexisting surgical instruments economically and with minimal designchanges to preserve compatibility of the surgical devices with currentgenerator platforms.

Additionally, embodiments of the generator 1002 may enable communicationwith instrument-based data circuits. For example, the generator 1002 maybe configured to communicate with a second data circuit contained in aninstrument (e.g., instrument 1024 or 1034) of a surgical device. Theinstrument interface circuit 1098 may comprise a second data circuitinterface 2010 to enable this communication. In one embodiment, thesecond data circuit interface 2010 may comprise a tri-state digitalinterface, although other interfaces may also be used. In certainembodiments, the second data circuit may generally be any circuit fortransmitting and/or receiving data. In one embodiment, for example, thesecond data circuit may store information pertaining to the particularsurgical instrument with which it is associated. Such information mayinclude, for example, a model number, a serial number, a number ofoperations in which the surgical instrument has been used, and/or anyother type of information. Additionally or alternatively, any type ofinformation may be communicated to second data circuit for storagetherein via the second data circuit interface 2010 (e.g., using thelogic device 2000). Such information may comprise, for example, anupdated number of operations in which the instrument has been usedand/or dates and/or times of its usage. In certain embodiments, thesecond data circuit may transmit data acquired by one or more sensors(e.g., an instrument-based temperature sensor). In certain embodiments,the second data circuit may receive data from the generator 1002 andprovide an indication to a user (e.g., an LED indication or othervisible indication) based on the received data.

In certain embodiments, the second data circuit and the second datacircuit interface 2010 may be configured such that communication betweenthe logic device 2000 and the second data circuit can be effectedwithout the need to provide additional conductors for this purpose(e.g., dedicated conductors of a cable connecting a handpiece to thegenerator 1002). In one embodiment, for example, information may becommunicated to and from the second data circuit using a 1-wire buscommunication scheme implemented on existing cabling, such as one of theconductors used transmit interrogation signals from the signalconditioning circuit 2002 to a control circuit in a handpiece. In thisway, design changes or modifications to the surgical device that mightotherwise be necessary are minimized or reduced. Moreover, becausedifferent types of communications implemented over a common physicalchannel can be frequency-band separated, the presence of a second datacircuit may be “invisible” to generators that do not have the requisitedata reading functionality, thus enabling backward compatibility of thesurgical device instrument.

In certain embodiments, the isolated stage 1052 may comprise at leastone blocking capacitor 2096-1 connected to the drive signal output 1060b to prevent passage of DC current to a patient. A single blockingcapacitor may be required to comply with medical regulations orstandards, for example. While failure in single-capacitor designs isrelatively uncommon, such failure may nonetheless have negativeconsequences. In one embodiment, a second blocking capacitor 2096-2 maybe provided in series with the blocking capacitor 2096-1, with currentleakage from a point between the blocking capacitors 2096-1, 2096-2being monitored by, for example, an ADC 2098 for sampling a voltageinduced by leakage current. The samples may be received by the logiccircuit 2000, for example. Based changes in the leakage current (asindicated by the voltage samples in the embodiment of FIG. 19), thegenerator 1002 may determine when at least one of the blockingcapacitors 2096-1, 2096-2 has failed. Accordingly, the embodiment ofFIG. 19 provides a benefit over single-capacitor designs having a singlepoint of failure.

In certain embodiments, the non-isolated stage 1054 may comprise a powersupply 2011 for outputting DC power at a suitable voltage and current.The power supply may comprise, for example, a 400 W power supply foroutputting a 48 VDC system voltage. The power supply 2011 may furthercomprise one or more DC/DC voltage converters 2013 for receiving theoutput of the power supply to generate DC outputs at the voltages andcurrents required by the various components of the generator 1002. Asdiscussed above in connection with the controller 1096, one or more ofthe DC/DC voltage converters 2013 may receive an input from thecontroller 1096 when activation of the “on/off” input device 1045 by auser is detected by the controller 1096 to enable operation of, or wake,the DC/DC voltage converters 2013.

Having described operational details of various embodiments of thesurgical systems 19 (FIG. 1), 190 (FIG. 10), 1000 (FIG. 16) operationsfor the above surgical systems 19, 190, 1000 may be further describedgenerally in terms of a process for cutting and coagulating tissueemploying a surgical instrument comprising an input device 406, 1009 andthe generator 1002. Although a particular process is described inconnection with the operational details, it can be appreciated that theprocess merely provides an example of how the general functionalitydescribed herein can be implemented by any one of the surgical systems19, 190, 1000. Further, the given process does not necessarily have tobe executed in the order presented herein unless otherwise indicated. Aspreviously discussed, any one the input devices 406, 1009 may beemployed to program the output (e.g., impedance, current, voltage,frequency) of the surgical devices 100 (FIG. 1), 120 (FIG. 10), 1002(FIG. 16), 1006 (FIG. 16).

FIGS. 20-22 illustrate various embodiments of logic flow diagrams of1200, 1300, 1400 related to a tissue algorithm for detecting when rapidheating of the ultrasonic end effector 1026 blade occurs and provide theopportunity for responding via the output indicator 412 (FIGS. 9, 11)and/or the output device 1047 (FIG. 16) (e.g., annunciation, modulationof power output and/or display of content). According to the presentdisclosure, when multiple reference numbers are used to described anelement such as “ultrasonic surgical instrument 100, 120, 1004,” itshould be understood to reference any one of the elements, such as, forexample, “ultrasonic surgical instrument 100,” or “ultrasonic surgicalinstrument 120,” or “ultrasonic surgical instrument 1004.”

In various embodiments, feedback may be provided by the output indicator412 shown in FIGS. 9 and 11 or the output device 1047 in FIG. 16. Thesefeedback devices (e.g., output indicator 412, output device 1047) areparticularly useful in applications where the tissue being manipulatedby the end effector 81 (FIG. 1), 810 (FIG. 10), 1026 (FIG. 16) is out ofthe user's field of view and the user cannot see when a change of stateoccurs in the tissue. The feedback device communicates to the user thata change in tissue state has occurred as determined in accordance withthe operations described with respect to the logic flow diagrams 700,800, 900, 1200, 1300, 1400 as they relate to corresponding tissuealgorithms. The feedback devices may be configured to provide varioustypes of feedback according to the current state or condition of thetissue. A change of state of the tissue may be determined based ontransducer and tissue measurements based on voltage, current, andfrequency measurements in accordance with the operations described withrespect to the logic flow diagrams 700, 800, 900 described above inconnection with FIGS. 15A-C and the logic flow diagrams 1200, 1300, 1400described below in connection with FIGS. 20-22.

In one embodiment, the logic flow diagrams 1200, 1300, 1400 may beimplemented as executable modules (e.g., algorithms) comprising computerreadable instructions to be executed by the processor 400 (FIGS. 9, 11,14) portion of the generator 30, 500 or the generator 1002 (FIGS. 16,17, 19). In various embodiments, the operations described with respectto the logic flow diagrams 1200, 1300, 1400 may be implemented as one ormore than one software component, e.g., program, subroutine, logic; oneor more than one hardware components, e.g., processor, DSP, PLD, PGA,FPGA, ASIC, circuit, logic circuit, register; and/or combinations ofsoftware and hardware. In one embodiment, the executable instructions toperform the operations described by the logic flow diagrams 1200, 1300,1400 may be stored in memory. When executed, the instructions cause theprocessor 400, the DSP processor 1074 (FIG. 19) or logic device 1066(FIG. 19) to determine a change in tissue state in accordance with theoperations described in the logic flow diagrams 1200, 1300, and 1400 andprovide feedback to the user by way of the output indicator 412 (FIGS.9, 11) or output indicator 1047 (FIGS. 16, 17). In accordance with suchexecutable instructions, the processor 400, DSP processor 1074, and/orlogic device 1066 monitors and evaluates the voltage, current, and/orfrequency signal samples available from the generator 30, 500, 1002 andaccording to the evaluation of such signal samples determines whether achange in tissue state has occurred. As further described below, achange in tissue state may be determined based on the type of ultrasonicinstrument and the power level that the instrument is energized at. Inresponse to the feedback, the operational mode of any one of theultrasonic surgical instruments 100, 120, 1004 may be controlled by theuser or may be automatically or semi-automatically controlled.

A brief summary of a tissue algorithm represented by way of the logicflow diagrams 1200, 1300, 1400 will now be described in connection withany one of the ultrasonic surgical instruments 100, 120, 1004 driven bya corresponding generator 30 (FIG. 1), 500 (FIG. 10), 1002 (FIG. 17). Inone aspect, the tissue algorithm detects when the temperature of theblade portion (and therefore resonance) of the ultrasonic end effector81 (FIG. 1), 810 (FIG. 10), 1026 (FIG. 17) is changing rapidly (of mostinterest is an increasing change). For a clamping or shears typeinstrument, this change may correspond to a common clinical scenario,among others, when minimal-to-no tissue, tissue debris or fluid isadjacent the blade and the blade is activated against the clamp arm,clamp pad or other suitable tissue biasing member. For non-clampingapplications where an instrument with or without a clamp arm andassociated mechanisms is used to effect tissue, this change correspondsto conditions where rapid heating occurs such as when the blade isactivated against bone or other hard materials or when excessive forceis used to couple the blade to tissue targets. These are illustrativecases; one can imagine other clinical scenarios where rapid bladeheating may occur and such a tissue algorithm as described here is ofbenefit.

The tissue algorithm represented by the logic flow diagrams 1200, 1300,1400 may be employed in conjunction with any of the generators 30, 500,1002 described herein, and other suitable generators such as the GEN 04,GEN 11 generators sold by Ethicon Endo-Surgery, Inc. of Cincinnati,Ohio, and related devices, systems, that may leverage the algorithm ortechnology disclosed herein. Accordingly, in the description of thetissue algorithm in conjunction with the flow diagrams 1200, 1300, 1400reference is made to the generators 30, 500, 1002 described inconnection with corresponding FIGS. 1-9, 10-13, and 16-19.

Accordingly, with reference now to FIGS. 1-14, the frequency of theblade/handpiece resonant system of any one of the ultrasonic surgicalinstruments 100, 120, 1004 is dependent on temperature. When, forexample, an ultrasonic shear type end effector cuts through a clampedpiece of tissue, the blade heats and thins the tissue until ultimatelyit cuts through the tissue. At this point, the blade resides against thetissue pad and, if clamp pressure remains between the two, the blade andpad interface will draw power via the mechanical or vibratory motion ofthe blade relative to the pad. The power “deposited” at the interfacewill be largely conducted into the blade tip as the pad material isquite insulative. It is this thermal energy that alters the stiffness ofthe blade tip and the system resonance will change accordingly due tothese localized (to the tip) conditions. The generator 30, 500, 1002tracks this resonance. The shears example illustrates one scenario forwhich the algorithm is of use. Additional scenarios are back-cuttingwith a shears device with the clamp arm closed, blade cutting againsttough or hard tissue, or any scenario in which knowing the thermalcondition of the blade end-effector is desired. A tissue algorithm thatapplies logic to this tracking of resonance and, therefore, blade tipthermal condition is now described in connection with logic flowdiagrams 1200, 1300, 1400 in FIGS. 20-22.

In addition, the description of the tissue algorithm described inconnection with logic flow diagrams 1200, 1300, 1400 will be accompaniedwith illustrative examples via data obtained using any one of theultrasonic surgical instruments 100, 120, 1004 comprising acorresponding generator 30, 500, 1002 described herein.

The tissue algorithm described in connection with logic flow diagrams1200, 1300, 1400 relies on the monitoring of electrical drive signals,especially those correlating to the resonant frequency of the drivesignal. The algorithm monitors the resonant frequency and its changewith time (i.e., the first derivative of frequency with respect totime). Throughout this disclosure, this change in frequency with time isreferred to as frequency slope. Frequency slope is calculated locally(from a time perspective) by calculating the change in frequency ofadjacent (or relatively near) data points and dividing by thecorresponding change in time. Because of signal transients, averaging orany of a multitude of applicable filtering or smoothing techniques (suchthat trends are more easily discernable and prevents turning on/offcondition sets rapidly) may be employed. The data plots shown in FIGS.62, 63, 64 illustrate the calculation of frequency slope and the use ofaveraging techniques (e.g., exponentially weighted moving average orEWMA) to obtain frequency slope values useful for control/monitoring.Other descriptions of frequency slope include, without limitation,“first derivative of frequency” and “frequency change with respect totime.”

FIG. 20 is a logic flow diagram 1200 of a tissue algorithm that may beimplemented in one embodiment of a generator 30, 500, 1002. At a generallevel, the tissue algorithm described in connection with logic flowdiagram 1200 assesses the electrical signals in real time against a setof logic conditions that correlate to events of interest (e.g., blade ofultrasonic instrument is rapidly heating). Accordingly, the generator30, 500, 1002 determines when a set of logic conditions occur andtriggers a corresponding set of responses. The terms “Condition Set” and“Response set” are defined follows:

(1) Condition Set—a set of logic conditions that electrical signals aremonitored against in real time.

(2) Response Set—one or more responses of the generator 30, 500, 1002system to a Condition Set having been met.

At 1202, the generator 30, 500, 1002 is placed in an ultrasonic drivemode in a ready state.

At 1204, the generator 30, 500, 1002 is activated at a predeterminedpower level N. When the user activates the surgical system 19, 190,1000, the corresponding generator 30, 500, 1002 responds by seeking thesurgical system 19, 190, 1000 resonance and then ramping the output tothe end effectors 81, 810, 1026 to the targeted levels for the commandedpower level.

At 1206, the tissue algorithm determines whether parameters associatedwith the tissue algorithm are in use by determining when at least oneCondition Sets/Response Sets flag is enabled. When no such flags areenabled, the algorithm proceeds along “NO” path where at 1208 thesurgical system 19, 190, 1000 is operated in normal ultrasonic mode andat 1210, the corresponding generator 30, 500, 1002 is deactivated whenthe tissue procedure is completed.

When at least one flag for setting Condition Sets/Response Sets isenabled, the algorithm proceeds along “YES” path and the generator 30,500, 1002 utilizes the tissue algorithm 1300 signal evaluation afterresetting a Timer X and Timer X latch. In one embodiment, the at leastone flag for setting Condition Sets/Response Sets may be stored in anEEPROM image of an instrument 100, 120, 1004 attached to the respectivegenerator 30, 500, 1002. The EEPROM flags for setting the ConditionSets/Response Sets to an enabled state are contained in TABLE 1.

TABLE 1 Enable/Disable Flag Value to Value for Functions for TissueAlgorithm Enable “Normal” Name Description Function Drive Condition Set1 If Condition Set 1 is met and this 1 0 Pulsing flag function isenabled, the generator pulses power per the pulsing parameters as a partof Response Set 1 Condition Set 1 If Condition Set 1 is met and this 1 0LCD display function is enabled, the generator flag LCD displays anassigned graphics screen as part of Response Set 1 Condition Set 1 IfCondition Set 1 is met and this 1 0 Audio flag function is enabled, thegenerator plays an assigned audio file as part of Response Set 1Condition Set 2 If Condition Set 2 is met and this 1 0 Pulsing flagfunction is enabled, the generator pulses power per the pulsingparameters as a part of Response Set 2 Condition Set 2 If Condition Set2 is met and this 1 0 LCD display function is enabled, the generatorflag LCD displays an assigned graphics screen as part of Response Set 2Condition Set 2 If Condition Set 2 is met and this 1 0 Audio flagfunction is enabled, the generator plays an assigned audio file as partof Response Set 2

In one embodiment, the tissue algorithm 1300 signal evaluation portionof the logic flow diagram 1200 utilizes two Condition Sets and each ofthese two Conditions Sets has a Response Set, which are described inmore detail in connection with logic flow diagrams 1300, 1400. Thetissue algorithm 1300 logic may be illustrated as follows: whenCondition Set 1 is met, Response Set 1 is triggered. Having twocondition sets enables a hierarchical response (differentiated responsesbased upon condition level) and also provides the ability to manage acomplicated series of events.

At 1210, responses for Condition Sets that are met are triggered. Loop1212 is repeated until the Condition Sets are met and the generator 30,500, 1002 is deactivated at 1214.

The pulsing response is more detailed and requires further explanationthan the relatively simple audio and LCD display responses. When apulsing response is triggered, the generator 30, 500, 1002 drives apulsed output as defined by the by the following four parameters:

(1) First Pulse Amplitude (EEPROM parameter, one value for each powerlevel)—the drive amplitude for the first pulse;

(2) First Pulse Time (EEPROM parameter)—the time over which the firstpulse amplitude is driven;

(3) Second Pulse Amplitude (EEPROM parameter, one value for each powerlevel)—the drive amplitude for the second pulse; and

(4) Second Pulse Time (EEPROM parameter)—the time over which the secondpulse amplitude is driven.

When driving a pulsed output, the generator 30, 500, 1002 drives thefirst pulse, then the second pulse and then repeats. The pulse amplitudemay be expressed in units of: percentage of the commanded power level'soutput current. The commanded power level may be set by the activationswitch (MIN or MAX) and the generator setting when MIN is activated.

FIG. 21 is a logic flow diagram 1300 of a signal evaluation tissuealgorithm portion of the tissue algorithm shown in FIG. 20 that may beimplemented in one embodiment of a generator. The tissue algorithmsignal evaluation flow shown in FIG. 21 shows the application of a “timeto wait” parameter 1304 and the calculation of a frequency slope (alsoreferred to as local frequency slope because it is a runningcalculation).

At 1302, the algorithm calculates the time since activation wasinitiated at 1204 (FIG. 20). This time is expressed as T_(Elapse), whichis T_(sytem)−T_(PowerOn). As previously discussed, when the useractivates the surgical system 19, 190, 1000, the corresponding generator30, 500, 1002 responds by seeking the resonance of the ultrasonic system100, 120, 1004 and then ramping the output to the corresponding endeffectors 81, 810, 1026 to the targeted levels for the commanded powerlevel.

During this time, the associated signal transients can make theapplication of algorithm logic difficult. The algorithm, therefore,utilizes the “time to wait” parameter 1304 that is stored in the EEPROMimage located in a hand piece portion of the ultrasonic surgicalinstrument 100, 120, 1004. The “time to wait” parameter 1304 (EEPROMparameter) is defined as the time at the beginning of an activationduring which the generator 30, 500, 1002 does not apply the tissuealgorithm to lessen the influence of resonance seek and drive rampsignal transients on algorithm logic. A typical “time to wait” parameter1304 value is about 0.050 to 0.600 seconds (50 to 600 msec).

At 1306, T_(Elapse) is compared to the “time to wait” parameter 1304value. When T_(Elapse) is less than or equal to the “time to wait”parameter 1304 value, the algorithm proceeds along “NO” path tocalculate at 1302 a new T_(Elapse). When T_(Elapse) is greater than the“time to wait” parameter 1304 value, the algorithm proceeds along “YES”path to evaluate the signal.

At 1308, the algorithm performs the Signal Evaluation/Monitoringfunction. As previously stated, one aspect of the function algorithm isto monitor frequency slope. In a physical sense, frequency slopecorrelates to heat flux into or out of the resonant system comprisingthe blade and the handpiece acoustical subassembly, such as theultrasonic systems 100, 120, 1004 disclosed herein. The changes infrequency and frequency slope during activation on tissue are dominatedby the changing conditions occurring at the end-effector (tissue dryingout, separating and blade contacting the clamp arm pad). When the bladeis being heated (i.e., heat flux into the blade), the frequency slope isnegative. When the blade is being cooled (i.e., heat flux out of theblade), the frequency slope is positive. Accordingly, the algorithmcalculates the slope between frequency data points, i.e., incomingfrequency data points 1310 (F_(t)) and previous F_(t) data points 1312.The calculated frequency slope also may be referred to as a localfrequency slope because it is a running calculation. The local frequencyslope may be referred to as F_(Slope) _(_) _(Freq), F_(t), which is thefrequency slope (F_(Slope) _(_) _(Freq)) at the resonance frequency(F_(t)). The local frequency slope may be routed to a Condition Set 1,Condition Set 2 1400, for example, for evaluation in accordance with theflow diagram 1400 shown in FIG. 22.

FIG. 22 is a logic flow diagram 1400 for evaluating condition sets forthe signal evaluation tissue algorithm shown in FIG. 21 that may beimplemented in one embodiment of a generator. The logic flow diagram1400 evaluates Condition Set X, where X is either 1 or 2, for example.

In accordance with the tissue algorithm, at 1402, the local frequencyslope calculated at 1308 (FIG. 21) is compared against a frequency slopethreshold parameter 1404 value for Condition Set X at Power Level N. Thefrequency slope threshold parameters 1404 may be stored in an EEPROMlocated in the attached instrument 100, 120, 1004, where one EEPROMparameter value is stored for each power level. When the local frequencyslope calculated at 1308 drops below the frequency slope thresholdparameter 1404 value, a first Response Set may be triggered at 1210(FIG. 20). When the blade is being heated at a relatively rapid rate,the frequency slope will become more negative and the tissue algorithmidentifies this condition by way of the frequency slope dropping belowthe frequency slope threshold parameter 1404 value. Again, the frequencyslope indicates the rate of thermal change or heat flux into or out ofthe blade.

In accordance with the tissue algorithm, also at 1402, the resonantfrequency is compared against a frequency threshold parameter 1406 valuefor Condition set X. The frequency threshold parameter 1406 value may bestored in an EEPROM located in the attached instrument 100, 120, 1004.When the resonant frequency drops below the threshold frequencyparameter 1406 value, a second Response Set may be triggered at 1210(FIG. 20). As a blade is continually heated, the frequency will continueto drop. A frequency threshold parameter 1406 value is intended toimprove algorithm robustness by providing additional information aboutthe thermal condition of the blade (in addition to the more dynamicindicator, the frequency slope). Frequency drop from some knowncondition such as room temperature gives a good indication of thethermal state of the resonant system relative to these known thermalconditions.

At 1402, when the frequency slope (F_(Slope) _(_) _(Freq)) is less thanthe frequency slope threshold parameter 1404 value and the resonantfrequency (F_(t)) is less than the frequency threshold parameter 1406value, the algorithm proceeds along “YES” path to 1408 to increment aTimer X (where X corresponds to the particular Condition Set beingevaluated by the tissue algorithm).

In comparing the electrical signals, e.g., the frequency slope(F_(Slope) _(_) _(Freq)) and the resonant frequency (F_(t)), againstrespective thresholds parameters 1404, 1406, borderline conditions wherethe signal bounces back-and-forth across the threshold can be taken intoconsideration as follows. In one aspect, the tissue algorithm employs a“required time before trigger” parameter 1412 value (which also may bestored in the instrument EEPROM) for the particular Condition Set X toaccount for this consideration. The “required time before trigger”parameter 1412 value is defined as the time required before trigger(EEPROM parameter)—required time for frequency slope and/or frequency tobe less than their respective thresholds for a Response Set to betriggered. This is intended to prevent rapid “back and forth” triggeringof a response. It may be useful, however, to track non-rapid “back andforth” triggering, which may occur.

Thus, at 1414 the algorithm determines whether the Timer X value isgreater than the “required time before trigger” parameter 1412 value forCondition Set X. When the Timer X value is greater than the “requiredtime before trigger” parameter 1412 value, the algorithm proceeds along“YES” path to set a latch for Condition Set X at 1416. Output 1418indicates that the Condition Set X is met. When the Timer X value isless than or equal to the “required time before trigger” parameter 1412value, the algorithm proceeds along “NO” path to indicate at output 1420that the Condition Set X is not met.

At 1402, when either the frequency slope (F_(Slope) _(_) _(Freq))greater than or equal to the frequency slope threshold parameter 1404value or the resonant frequency (F_(t)) is greater than then or equal tothe frequency threshold parameter 1406 value, the algorithm proceedsalong “NO” path to reset the Timer X at 1410 (where X corresponds to theparticular Condition Set being evaluated by the tissue algorithm).

For additional robustness, two latching parameters are employed by thealgorithm. Without the use of latching, the algorithm is configured toend a response set when either (a) the system is deactivated or (b) whenthe signal or signals are no longer below their respective thresholds.Two latching parameters can be utilized. They are a “minimum latch time”parameter 1422 and a “cross-back frequency slope threshold” parameter1424. These latch parameters 1422, 1424 are important for robustnessaround: (a) clamp arm pad surfaces that become more lubricious withelevated temperature and (b) pulsing output where signal transients atthe pulse transitions are expected.

The minimum latch time parameter 1422 (EEPROM parameter) can be definedas the minimum amount of time for response(s) to a Condition Set X to betriggered. Considerations for minimum latch time include: (a) the lengthof time required to play a triggered audible response (e.g., in oneembodiment, a “pre-alert” WAV audio file may be about 0.5 seconds long),(b) the typical (about 0.5 to 1.0 sec) or extreme (about 1.5 to 2.0 sec)user response times for an event, or (c) the typical tissue re-grasptime for a multi-cut (known as “marching”) application (about 1.1-2.0seconds with a mean of about 1.6 seconds).

The cross-back frequency slope threshold parameter 1424 (EEPROMparameter) can be defined as the frequency slope threshold above which atriggered response stops (i.e., is no longer triggered). This providesfor a higher “cross-back-over” frequency slope threshold that is taskedwith distinguishing between activating against the pad and jaw opened(versus distinguishing between activating on tissue and activating onthe pad).

In accordance with the tissue algorithm portion represented by logicflow diagram 1400, after the Timer X is reset at 1410, at 1426, thetissue algorithm determines whether either the latch for Condition Set Xor the Cross-back Frequency Slope Latch is set. When both latches arenot set, the algorithm proceeds along “NO” to indicate at output 1420that the Condition Set X is not met. When either one of the latches isset, the algorithm proceeds along “YES” path to 1428.

At 1428, the algorithm determines whether the Latched Time for ConditionSet X is greater than the minimum latch time parameter 1422 value forCondition Set X and whether the frequency slope (F_(Slope) _(_) _(Freq))is greater than the cross-back frequency slope threshold parameter 1424value the algorithm proceeds along “YES” path to reset the Latch forTimer X at 1430 and to indicate at output 1420 that the Condition Set Xis not met. When the Latched Time for Condition Set X is less than orequal to the minimum latch time parameter 1422 value for Condition Set Xand the frequency slope (F_(Slope) _(_) _(Freq)) less than or equal tothe cross-back frequency slope threshold parameter 1424 value thealgorithm proceeds along “NO” path to indicate at output 1432 that theCondition Set X is met.

As shown in FIGS. 21 and 22, there are two identical Condition Sets 1and 2 from a flow perspective. These Conditions Sets 1 and 2 havereplicate sets of parameters as contained in TABLE 2. Algorithmparameters that are shared by the Condition Sets 1 and 2 are containedin TABLE 3.

TABLE 2 contains a summary of the replicated algorithm EEPROM parametersfor each of the Condition Sets and the number parameters per ConditionSet.

TABLE 2 Algorithm EEPROM Parameter Summary, Replicated Parameters forEach of the Condition Sets Replicated Parameters for Each # ofParameters per of the Condition Sets Condition Set Required time beforetriggered 1 Minimum latch time 1 Frequency Slope Thresholds (one foreach 5 power level) Frequency Threshold 1

TABLE 3 contains a summary of the shared algorithm EEPROM parameters foreach of the Condition Sets (not replicated) and the number parameters.

TABLE 3 Algorithm EEPROM Parameter Summary, Common Parameters to allCondition Sets Parameters Shared by Condition Sets (not replicated) # ofParameters Time to wait 1 Cross-back Frequency Slope Threshold 1 FirstPulse Amplitudes (one for each power 5 level) First Pulse Time 1 SecondPulse Amplitudes (one for each power 5 level) Second Pulse Time 1

For clarity of disclosure, the tissue algorithm described in connectionwith the logic flow diagrams 1200, 1300, 1400 shown in respective FIGS.20-22 will now be described in terms of four examples. The basicapplication of the tissue algorithm includes the monitoring of frequencyslope, resonant frequency, or both against their respective thresholds.Accordingly, a first example includes the monitoring of frequency slopeagainst its respective threshold and is illustrated in FIGS. 23-28. Asecond example includes the monitoring of resonant frequency against itsrespective threshold and is illustrated in FIGS. 29-31. A third exampleincludes the monitoring both the frequency slope and the resonantfrequency, against their respective threshold and is illustrated inFIGS. 32-34. Finally, a fourth example also includes the monitoring bothof the frequency slope and the resonant frequency, against theirrespective threshold.

Example 1: Monitoring Frequency Slope Against Respective Threshold

A first example case includes the monitoring of frequency slope againsta respective threshold is illustrated with reference to FIGS. 23-28. Thefirst example, and most simple, is the example of triggering a ResponseSet based only on the frequency slope. TABLE 4 contains representativeparameters for this objective for surgical instruments such as any oneof the surgical instruments 19, 190, 1000 disclosed herein comprising acorresponding ultrasonic instrument such as ultrasonic instruments 100,120, 1004 disclosed herein.

TABLE 4 Representative Parameters for Triggering an Audio Indication byFrequency Slope Threshold Only (one Condition Set utilized) ParameterValue* Condition Set 1 Pulsing flag 0 Condition Set 1 LCD display flag 0Condition Set 1 Audio flag 1 Required time before triggered, ConditionSet 1 50 msec Minimum latch time, Condition Set 1  0 msec* FrequencySlope Thresholds (one for each level 5: −0.060 kHz/sec power level),Condition Set 1 level 4: −0.053 kHz/sec level 3: −0.045 kHz/sec level 2:−0.038 kHz/sec level 1: −0.030 kHz/sec Frequency Threshold, ConditionSet 1 56,000 Hz* Time to wait 100 msec  Cross-back Frequency SlopeThreshold −0.020 kHz/sec First Pulse Amplitudes (one for each powerlevel) N/A First Pulse Time N/A Second Pulse Amplitudes (one for eachpower N/A level) Second Pulse Time N/A *These parameter values are setto an appropriate extreme such that they do not effectively take part inthe logic flow (e.g., set to always be “true”).

FIGS. 23-25 show signal data produced by a generator with therepresentative/illustrative parameters contained in TABLE 4. Thegenerator may be similar to any one of the generators 30, 500, 1002disclosed herein, which forms a portion of the respective surgicalsystems 19, 190, 1000 operating in ultrasonic mode (e.g., ultrasonicsystem 19, 190, 1000) applied on tissue in accordance with the presentdisclosure.

The use of only the frequency slope to trigger a Response Set may befurther demonstrated in the “burn-in” scenario or test. FIGS. 26-28 showsignal data produced by a generator with the representative/illustrativeparameters contained in TABLE 4 during a “burn-in” scenario or test. A“burn-in” simulates the use case where a user activates a shears typeultrasonic surgical instrument without intervening tissue (e.g.,back-cutting with jaws closed). This test also may be useful forquantifying device characteristics, such as, for example, “responsetime.”

The response time of an ultrasonic instrument may be defined as the timerequired for an ultrasonic system (instrument, handpiece, and generatorwith tissue algorithm) to respond to the clamp arm pad coming intocontact with the blade. The ultrasonic system is usually initiallyactivated “in-air” (i.e., unloaded), the clamp arm is closed against theblade and held for a period of time and then the clamp arm is opened andthe ultrasonic system is deactivated. The response time is the timebetween the point at which the quiescent power (power in-air) begins tochange due to the clamp arm pad initiating contact with the blade andthe point at which the Response Set is triggered. This is also a testthat enables quantification of the rate of cooling—the higher the rateof cooling (assuming similar convective boundary conditions) the morethermal energy or residual heat there is in the blade. The rate ofcooling is proportional to the frequency slope (to reinforce: a positivefrequency slope value correlates to the instantaneous heat flux out ofthe blade). As will be detailed later, the rate of cooling also may bemonitored and used for control purposes so that, for example, if therate of cooling as defined by a positive frequency slope is greater thana threshold value, one knows that the blade is “carrying” a large amountof thermal energy and is dissipating it rapidly.

FIG. 23 is a graphical representation 1500 of frequency slope versustime of a waveform 1502 of one embodiment of a generator during atypical tissue cut. Frequency slope (kHz/sec) is shown along thevertical axis and time (Sec) is shown along the horizontal axis for atypical tissue cut using any one of the ultrasonic systems comprisingcorresponding ultrasonic surgical instruments set on power level 5. Thefrequency slope threshold 1504 used for this application was −0.06kHz/sec and is shown by the horizontal dashed line. The verticaldash-dot line 1506 shows the time (2.32 seconds) that the tissue beganto separate, and the vertical dashed line 1508 shows the time (2.55seconds) at which the ultrasonic system triggered a Response Set (inthis case, per TABLE 4, an audible sound only).

FIG. 23A is a graphical representation of a second time derivative offrequency (slope of frequency slope) versus time waveform 1503 (shown indashed line) superimposed over the waveform 1502 shown in FIG. 23 of oneembodiment of a generator during a typical tissue cut.

FIG. 24 is a graphical representation 1510 of frequency versus timewaveform 1512 of one embodiment of a generator during a typical tissuecut as it relates to the graphical representation 1500 shown in FIG. 23.Resonant frequency (kHz) is shown along the vertical axis and time (Sec)is shown along the horizontal axis for the typical tissue cut using anyone of the ultrasonic systems set on power level 5. The verticaldash-dot line 1506 shows the time (2.32 seconds) that the tissue beganto separate, and the vertical dashed line 1508 shows the time (2.55seconds) at which the ultrasonic system triggered a Response Set (inthis case, an audible sound only).

FIG. 25 is a graphical representation 1514 of power consumption versustime waveform 1514 of one embodiment of a generator during a typicaltissue cut as it relates to the graphical representation 1500 shown inFIG. 23. Power (W) is shown along the vertical axis and time (Sec) isshown along the horizontal axis for the typical tissue cut using any oneof the ultrasonic systems set on power level 5. The vertical dash-dotline 1506 shows the time (2.32 seconds) that the tissue began toseparate, and the vertical dashed line 1508 shows the time (2.55seconds) at which the ultrasonic system triggered a Response Set (inthis case, an audible sound only).

FIG. 26 is a graphical representation 1516 of frequency slope versustime waveform 1518 of one embodiment of a generator during a burn-intest. The parameters for this test are consistent with those containedin TABLE 4. Frequency slope (kHz/sec) is shown along the vertical axisand time (Sec) is shown along the horizontal axis for a typical tissuecut using any one of the ultrasonic systems set on power level 5. Thefrequency slope threshold 1504 used for this application was −0.06kHz/sec as is shown by the horizontal dashed line. The vertical dottedline 1524 shows the point in time (2.49 seconds) that the quiescentpower begins to change due to clamping, the vertical dash-dot line 1506shows the time (2.66 seconds) at which power has completed ramp-up, andthe vertical dashed line 1508 shows the time (2.72 seconds) that theultrasonic system triggered a Response Set (in this case, an audiblesound only). As shown in the graphical representation 1516, thefrequency slope at 1520 correlates to the rate of cooling or heat fluxout of the blade. Also, the response time 1522 of the ultrasonic systemis measured as the time lapse between the point in time (2.49 seconds)that the quiescent power begins to change due to clamping and the time(2.72 seconds) that the ultrasonic system triggered a Response Set.

FIG. 27 is a graphical representation 1524 of a frequency versus timewaveform 1526 of one embodiment of a generator during a burn-in test asit relates to the graphical representation 1516 shown in FIG. 26.Resonant frequency (kHz) is shown along the vertical axis and time (Sec)is shown along the horizontal axis for the typical tissue cut using anyone of the ultrasonic systems set on power level 5.

FIG. 28 is a graphical representation 1528 of a power consumption versustime waveform 1530 of one embodiment of a generator during a burn-intest as it relates to the graphical representation 1516 shown in FIG.26. Power (W) is shown along the vertical axis and time (Sec) is shownalong the horizontal axis for the typical tissue cut using any one ofthe ultrasonic systems set on power level 5.

Example 2: Triggering a Response Set Based Only on the FrequencyThreshold

A second example case includes triggering a Response Set based only onthe frequency threshold with reference to FIGS. 29-35. TABLE 5 containsrepresentative parameters for this objective in connection with surgicalinstruments such as any one of the surgical instruments 19, 190, 1000disclosed herein comprising corresponding ultrasonic instruments such asthe ultrasonic instrument 100, 120, 1004 disclosed herein. It will beappreciated that triggering via frequency threshold may be of limitedutility as it is less indicative of dynamic end-effector conditions andis presented herein for completeness of disclosure. The inclusion offrequency slope in the tissue algorithm discussed in connection withlogic flow diagrams 1200, 1300, 1400 is intended for use in combinationlogic (combined with use of the frequency slope threshold) which iscovered in the next section of this specification.

TABLE 5 Representative Parameters for Triggering an Audio Indication byFrequency Threshold Only (one Condition Set utilized) Parameter Value*Condition Set 1 Pulsing flag 0 Condition Set 1 LCD display flag 0Condition Set 1 Audio flag 1 Required time before triggered, ConditionSet 1 50 msec Minimum latch time, Condition Set 1  0 msec* FrequencySlope Thresholds (one for each power level 5: 1.00 kHz/sec* level),Condition Set 1 level 4: 1.00 kHz/sec* level 3: 1.00 kHz/sec* level 2:1.00 kHz/sec* level 1: 1.00 kHz/sec* Frequency Threshold, Condition Set1 55,100 Hz Time to wait 100 msec  Cross-back Frequency Slope Threshold−1.00 kHz/sec* First Pulse Amplitudes (one for each power N/A level)First Pulse Time N/A Second Pulse Amplitudes (one for each N/A powerlevel) Second Pulse Time N/A *These parameter values are set to anappropriate extreme such that they do not effectively take part in logicflow (e.g., set to always be “true”)

FIGS. 29-34 show waveforms produced by a generator with therepresentative/illustrative parameters contained in TABLE 5. Thegenerator may be similar to any one of the generators 30, 500, 1002disclosed herein, which forms a portion of the respective surgicalsystems 19, 190, 1000 operating in ultrasonic mode (e.g., ultrasonicsystem 19, 190, 1000) applied on tissue in accordance with the presentdisclosure.

The selection of 55,100 Hz as the frequency threshold in TABLE 5 wasbased on test data for two abuse cases: (1) where an ultrasonicinstrument is activated against the tissue pad for a prolonged period oftime; and (2) where an ultrasonic instrument is used to make 10successive cuts on excised porcine jejunum tissue as quickly as possiblewhile keeping the generator running throughout. Each of these two abusecases will be discussed in more detail with reference to respective FIG.29 and FIGS. 30-31A-C.

FIG. 29 is a graphical representation 1600 of frequency change 1602 overtime of waveforms of several generators during a burn-in test. Frequencychange (kHz) after X seconds of burn-in is shown along the vertical axisand ultrasonic surgical instrument device number is shown along thehorizontal axis. FIG. 29 shows frequency change data after prolongedburn-ins of an ultrasonic surgical instrument where the ultrasonicsurgical instrument is activated against the tissue pad for a prolongedperiod of time (a prolonged burn-in). The selection of 55,100 Hz limitsthis condition to no more than a 4 second time span or a frequency dropof about a 700 Hz from a nominal room temperature resonant frequency of55,800 Hz. Frequency change data 16021, 16022, 16023, 16024 was pulledfrom the generator 30, 500, 1002 data at corresponding 1, 2, 3, and 4seconds into the burn-in. The nominal start frequency for the fiveultrasonic surgical instruments was 55.8 kHz (blades started at roomtemperature). The second and fifth devices did not run long enough togenerate a full set of data for all times.

FIG. 30 is a graphical representation 1604 of normalized combinedimpedance, current, and frequency versus time waveforms of and powerconsumption, energy supplied, and temperature for one embodiment of agenerator coupled to a corresponding ultrasonic instrument used to make10 successive cuts on tissue (e.g., on excised porcine jejunum tissue)as quickly as possible while keeping the generator running throughout.This data and the methods used to obtain it represent abusive useconditions.

The representative data in FIG. 30 is shown more clearly with referenceto FIGS. 31A-C. FIG. 31A is a graphical representation 1606 of impedanceversus time waveform 1608 and current versus time waveform 1610 of oneembodiment of a generator during successive tissue cuts over a period oftime. Impedance (Ohm) and Current (mA) are shown along the vertical axisand time (Sec) along the horizontal axis.

FIG. 31B is a graphical representation 1612 of resonant frequencywaveform 1614 versus time of a signal of one embodiment of a generatorduring successive tissue cuts over a period of time. Resonant frequency(kHz) is shown along the vertical axis and time (Sec) along thehorizontal axis.

FIG. 31C is a graphical representation 1616 of a power waveform 1618,energy waveform 1620, and temperature waveform 1622 versus time of oneembodiment of a generator during successive tissue cuts over a period oftime. Power (W), Energy (J), and Temp (C) are shown along the horizontalaxis and time (Sec) along the horizontal axis.

Accordingly, with reference now to FIGS. 31A-C, as shown in thegraphical representation 1612, it can be seen that after the resonantfrequency curve 1614 has dropped 700 Hz (from 55.8 kHz to 55.1 kHz) at1615 on the third cut (which is a particularly abusive cut wherein thetissue was tip loaded. After the resonance frequency waveform 1614 hasdropped 700 Hz (from 55.8 kHz to 55.1 kHz) on the third cut, theultrasonic instrument begins to saturate the generator and the currentwaveform 1610 dips slightly in all successive cuts. Since the drivecurrent waveform 1610 is proportional to blade tip displacement, adipping current waveform 1610 results in slower speed of tissue effectand therefore a lower energy deposition rate (and lower rate of heating,i.e., frequency slope is less negative). Management of this change dueto dipping current waveform 1610 within an application sequence ispossible using both frequency change and frequency slope change as willbe described in connection with Examples 3 and 4 in subsequent sectionsof this specification.

FIG. 32 is a combined graphical representation 1630 of a frequencywaveform 1632, weighted frequency slope waveform 1634 (calculated viaexponentially weighted moving average with an alpha value of 0.1), andtemperature waveform 1636 versus time generated by a generator similarto one embodiment of the generators described herein. The ultrasonicsystem had a room temperature resonant frequency (longitudinal mode)slightly higher than that for which TABLE 5 was constructed. Therefore,the frequency threshold 1633 was increased accordingly from the 55,100Hz shown in TABLE 5 to about 55,200 Hz shown in FIG. 33 as indicated bythe dashed line. The activation was performed on tissue (e.g., onexcised porcine jejunum tissue) with an ultrasonic system having a roomtemperature resonance of about 55.9 kHz set on power level 5. Tissueseparation occurs at 6.25 seconds; one side of the tissue separates fromthe blade at about 8 seconds; and full separation occurs at about 10seconds. FIG. 33 is a graphical representation of a frequency versustime waveform 1632 of one embodiment of a generator 30, 500, 1002.Frequency (kHz) is shown along the vertical axis and Time (Sec) is shownalong the horizontal axis. FIG. 33 shows the example of using afrequency threshold 1633 only using parameters consistent with thoseshown in TABLE 5, but adjusted to about 55,200 Hz as indicated by thedashed line 1633. The resonant frequency 1632 crosses the frequencythreshold 1633 (dashed horizontal line—set at 700 Hz below roomtemperature resonance) at about 11 seconds and a Response Set may betriggered at this time.

FIG. 34 is a graphical representation 1634 of weighted frequency slopeversus time waveform 1634 of one embodiment of a generator. Weightedfrequency slope (kHz/Sec) is shown along the vertical axis and Time(Sec) is shown along the horizontal axis. The frequency slope waveform1634 is calculated via exponentially weighted moving average with analpha value of 0.1. In FIG. 34, the frequency slope waveform 1634crosses the frequency slope threshold 1635 (dashed horizontal line) anda Response Set may be triggered at about 5.8 seconds.

The remaining Examples 3 and 4 relate to the use of multiple ConditionSets, which require a more complex application of the tissue algorithmand includes the monitoring of frequency slope and/or frequency againsttheir respective thresholds and may include a hierarchical approach totriggering response sets.

Example 3: Triggering a Response Set Based on Both the Frequency SlopeThreshold and the Frequency Threshold

A third example case includes triggering a Response Set based on boththe frequency slope threshold and the frequency threshold. TABLE 6contains representative parameters for this objective in connection withsurgical instruments such as any one of the surgical instruments 19,190, 1000 disclosed herein comprising corresponding ultrasonicinstruments such as the ultrasonic instruments 100, 120, 1004 disclosedherein.

TABLE 6 Representative Parameters for Triggering Audio Indications byFrequency Slope and Frequency Thresholds (two Condition Sets utilized)Parameter Value* Condition Set 1 Pulsing flag 0 Condition Set 1 LCDdisplay flag 0 Condition Set 1 Audio flag 1 Condition Set 2 Pulsing flag0 Condition Set 2 LCD display flag 0 Condition Set 2 Audio flag 1Required time before triggered, Condition Set 1 50 msec Minimum latchtime, Condition Set 1  0 msec* Frequency Slope Thresholds (one for eachpower   level 5: −0.060 kHz/sec level), Condition Set 1   level 4:−0.053 kHz/sec   level 3: −0.045 kHz/sec   level 2: −0.038 kHz/sec  level 1: −0.030 kHz/sec Frequency Threshold, Condition Set 1 56,000Hz* Required time before triggered, Condition Set 2 50 msec Minimumlatch time, Condition Set 2  0 msec* Frequency Slope Thresholds (one foreach power level 5: 1.00 kHz/sec* level), Condition Set 2 level 4: 1.00kHz/sec* level 3: 1.00 kHz/sec* level 2: 1.00 kHz/sec* level 1: 1.00kHz/sec* Frequency Threshold, Condition Set 2 55,100 Hz  Time to wait100 msec  Cross-back Frequency Slope Threshold −0.020 kHz/sec FirstPulse Amplitudes (one for each power level) N/A First Pulse Time N/ASecond Pulse Amplitudes (one for each power N/A level) Second Pulse TimeN/A *These parameter values are set to an appropriate extreme such thatthey do not effectively take part in logic flow (e.g. set to always be“true”)

In this case of Example 3, a tiered or hierarchical response isdemonstrated. The combined logic of the frequency slope threshold andthe frequency threshold will be illustrated using the same graphicalrepresentations shown in FIGS. 32-34. In FIG. 34, Condition Set 1 istriggered by the frequency slope waveform 1634 crossing the frequencyslope threshold 1635 value at about 6 seconds. The Response Set forCondition Set 1 may include a low level audible indicator, for example.As the user continues to activate the instrument with minimalintervening tissue, Condition Set 2 is triggered as the resonantfrequency drops below the frequency threshold 1633 at about 11 secondsas shown in FIG. 33. The Response Set for Condition Set 2 may be anelevated audible indicator, for example.

Example 4: Triggering a Response Set Based on Both the Frequency SlopeThreshold and the Frequency Threshold

A fourth example extends to the application of both frequency andfrequency slope thresholds during abusive conditions of the surgicalinstrument. For various reasons, the frequency slope signal levels maydiminish (i.e., become less negative) with extended application.

In abusive conditions, frequency, frequency slope, and current waveformsmay deviate from normal operation may be generated while the ultrasonicinstrument is constantly activated at a power level 5, where the jaws ofthe ultrasonic instrument were opened for 1 second, then closed for 1second and repeated for 17 cycles.

When an ultrasonic instrument is activated multiple times directlyagainst the pad, the characteristic frequency slope waveform in a firstregion before the generator saturates becomes less negative than in asecond after the generator saturates due, in large part, to the systemefficiency and resulting displacement/current drop. In thenon-saturation region of the frequency slope waveform, the ultrasonicsystem has not yet saturated and current is maintained at or near thetarget current for power level 5. In the saturation region of thefrequency slope waveform, the current (and therefore blade tipdisplacement) continually drops causing the frequency slope to increase(rate of heating drops). Note that at after several abusive cycles,e.g., the fourth abuse cycle, which is the approximate demarcationbetween the non-saturation and saturation regions, the resonantfrequency drops consistent with FIGS. 29-31A-C. Separate Conditions Setsfor each of the non-saturation and saturation regions may be applied. Afirst frequency slope threshold may be employed in the non-saturationregion when resonant frequency conditions are above a predeterminedfrequency threshold and a second, less negative frequency slopethreshold may be employed in the saturation region when resonantfrequency conditions are below the same predetermined frequencythreshold.

A weighted frequency slope (kHz/sec) versus time waveform may be of oneembodiment of a generator. When the instrument is used abusiveconditions against the pad, the characteristic frequency slope waveformin the non-saturation region becomes less negative than in thesaturation region due to material softening and a correspondingreduction in pad coefficient of friction. In the non-saturation regionof the frequency slope waveform corresponds to when the tissue pad hasnot yet begun to heat significantly. In the saturation region of thefrequency slope waveform, the pad begins to soften and the interfacebetween the blade and the pad becomes more lubricious causing thefrequency slope waveform to increase (rate of heating drops). SeparateConditions Sets for each of the non-saturation and saturation regionsmay be warranted. A first frequency slope threshold may be employed inthe non-saturation region when resonant frequency conditions are above apredetermined frequency slope threshold and a second, less negativefrequency slope threshold may be employed in the saturation region whenthe resonant frequency is below the same predetermined frequency slopethreshold.

Another example case is now considered. TABLE 7 contains parameters foran ultrasonic instrument where two Condition Sets are used to accountfor diminishing frequency slope signal levels due to system saturationand dropping current.

TABLE 7 Representative Parameters for Triggering Audio Indications byFrequency Slope and Frequency Thresholds, accounting for diminishingfrequency slope due to system saturation (two Condition Sets utilized)Parameter Value* Condition Set 1 Pulsing flag 0 Condition Set 1 LCDdisplay flag 0 Condition Set 1 Audio flag 1 Condition Set 2 Pulsing flag0 Condition Set 2 LCD display flag 0 Condition Set 2 Audio flag 1Required time before triggered, Condition Set 1 50 msec Minimum latchtime, Condition Set 1  0 msec* Frequency Slope Thresholds (one for eachpower level 5: −0.060 kHz/sec level), Condition Set 1 level 4: −0.053kHz/sec level 3: −0.045 kHz/sec level 2: −0.038 kHz/sec level 1: −0.030kHz/sec Frequency Threshold, Condition Set 1 56,000 Hz* Required timebefore triggered, Condition Set 2 50 msec Minimum latch time, ConditionSet 2  0 msec* Frequency Slope Thresholds (one for each power level 5:−0.045 kHz/sec level), Condition Set 2 level 4: −0.038 kHz/sec level 3:−0.030 kHz/sec level 2: −0.024 kHz/sec level 1: −0.020 kHz/sec FrequencyThreshold, Condition Set 2 55,100 Hz  Time to wait 100 msec  Cross-backFrequency Slope Threshold −0.020 kHz/sec First Pulse Amplitudes (one foreach power level) N/A First Pulse Time N/A Second Pulse Amplitudes (onefor each power N/A level) Second Pulse Time N/A *These parameter valuesare set to an appropriate extreme such that they do not effectively takepart in logic flow (e.g., set to always be “true”)

The data generated for this example run were generated using anultrasonic instrument to make ten successive cuts in jejunum tissue asquickly as possible. Using the parameter values from TABLE 7, theFrequency vs. Time plots for the example sample case are shown in FIGS.35-36.

FIG. 35 is a graphical representation 1800 of a frequency versus timewaveform 1802 of one embodiment of a generator over ten cuts on tissue(e.g., jejunum tissue) and a graphical representation 1804 of atemperature versus time waveform 1805. For the graphical representation1800, Frequency (Hz) is shown along the vertical axis and Time (Sec) isshown along the horizontal axis. For the graphical representation 1804,Temperature (° F.) is shown along the vertical axis and Time (Sec) isshown along the horizontal axis.

FIG. 36 is a graphical representation 1805 of the frequency versus timewaveform 1802 shown in FIG. 35 of one embodiment of a generator over tencuts on tissue (e.g., jejunum tissue) with activation of interveningtissue at portions indicated by reference number 1806. Frequency (Hz) isshown along the vertical axis and Time (Sec) is shown along thehorizontal axis.

The frequency waveform 1802 shown in FIGS. 35 and 36 is for the examplecase using two Condition Sets to account for diminishing frequency slopedue to electrical system saturation (diminishing displacement). Notethat this is the same test run as is shown in FIGS. 29-31A-C. In FIG.36, the highlighted portions 1806 indicates activation with interveningtissue (frequency drops, shape of local frequency curve related todryness of tissue—shallow start slope, steepens as tissue dries), thehighlighted portions 1808 indicate activation with minimal or nointervening tissue (local frequency slope very steep, curve shape ismore linear, steepens gradually), the section of the curve with nohighlighted portions 1810 indicates time within which the device isbeing repositioned for the next cut, blade cools in air and coolsrapidly when placed on tissue (frequency rises).

FIG. 37 is a graphical representation 1812 of a frequency slope versustime waveform 1814 of one embodiment of a generator over ten cuts onjejunum tissue. Frequency slope (kHZ/Sec) is shown along the verticalaxis and Time (Sec) is shown along the horizontal axis. Region B of thefrequency slope waveform 1814 shows the area of the ten cut run whereCondition Set 2 is triggered prior to Condition Set 1 for the first timeduring the ten cut run (frequency is below 55.1 kHz and frequency slopeis less than −0.045 kHz/sec). The condition illustrated in Region B,where Condition Set 2 is triggered prior to Condition Set 1, is desiredbecause the ultrasonic system is consistently saturating by this pointin the run (voltage is saturating and current is diminished resulting indiminished displacement and, therefore, diminished rate of heatingrequiring a greater frequency slope threshold).

FIG. 38 is a graphical representation 1816 of a power versus timewaveform 1818 representative of power consumed by a one embodiment of agenerator over ten cuts on tissue (e.g. jejunum tissue). Power (W) isshown along the vertical axis and Time (Sec) is shown along thehorizontal axis.

FIG. 39 is a graphical representation 1820 of a current versus timewaveform 1822 of one embodiment of a generator over ten cuts on jejunumtissue. Current (mA) is shown along the vertical axis and Time (Sec) isshown along the horizontal axis.

Having described the basic application of the tissue algorithm discussedin connection with the logic flow diagrams 1200, 1300, 1400 shown inFIGS. 20-22 in terms of monitoring the frequency slope, resonantfrequency, or both against their respective thresholds, the discussionnow turns to a description of the latching logic and corresponding useas it relates to the tissue algorithm. The motivations for adding thelatching logic to the tissue algorithm are: (a) to prevent a ConditionSet from resetting (Condition Set changes from true to false) due to ablade/pad interface becoming more lubricious during a blade on pad abusecondition; and (b) to prevent a Condition Set from resetting (ConditionSet changes from true to false) due to pulsed activation where periodsof rapid heating are interweaved with periods of less rapid heating(sections of heat flux into the blade and sections of heat flux out ofthe blade are interweaved). The first and second of these motivationsare shown in FIGS. 48 and 49 illustrate, respectively. As definedearlier in this disclosure, the two latch parameters addressing thesemotivations are “cross-back frequency slope threshold” as shown in FIG.40 and “minimum latch time.” For completeness of disclosure, FIG. 43shows calculated frequency slope curves for the pulsed run shown inFIGS. 41 and 42A-C.

FIG. 40 is a graphical representation 1900 of a “cross-back frequencyslope threshold” parameter in connection with frequency slope versustime waveform 1902. As shown in FIG. 40, the “frequency slope threshold”1904 is shown by the horizontal dashed line at −0.15 kHz/sec. The“cross-back frequency slope threshold” 1906 is shown by the horizontaldash-dot line at −0.02 kHz/sec. In this instance, the Condition Set ismet and a Response Set is triggered when the local calculated frequencyslope crosses the “frequency slope threshold” as shown by arrow 1908pointing down. The Condition Set is not met (Response Set is no longertriggered) when the local calculated frequency slope crosses over the“cross-back frequency slope threshold” as shown by arrow 1910 pointingup. Note that without using the “cross-back over frequency slopethreshold” in this case, the Response Set would not have been triggeredwhen the local frequency slope crossed back over the horizontal dashedline 1904 at about 4.7 seconds shown at cross over point 1911.

FIG. 41 is a combined graphical representation 1920 of a pulsedapplication of one embodiment of an ultrasonic instrument on an excisedcarotid artery showing normalized power, current, energy, and frequencydata plotted versus time.

FIG. 42A is a graphical representation 1921 of an impedance versus timewaveform 1922 and a current versus time waveform 1924 of one embodimentof a generator during successive tissue cuts over a period of time. Theimpedance (Ohms) and current (mA) is shown along the vertical axis andTime (Sec) is shown along the horizontal axis.

FIG. 42B is a graphical representation 1923 of a frequency versus timewaveform 1925 of one embodiment of a generator during successive tissuecuts over a period of time. Frequency (kHz) is shown along the verticalaxis and Time (Sec) is shown along the horizontal axis.

FIG. 42C is a graphical representation 1930 of power waveform 1926,energy waveform 1927, a first temperature waveform 1928 and a secondtemperature waveform 1929 plotted versus time as of one embodiment of agenerator during successive tissue cuts over a period of time. Power(W), Energy (J), and Temperature (° C.) are shown along the verticalaxis and Time (Sec) is shown along the horizontal axis.

FIGS. 42A-C show a pulsed application of an ultrasonic instrument on anexcised carotid artery where the First Pulse Time is 1 second, the FirstPulse Amplitude is 100% of power level 3 output current. The SecondPulse Time is 1.5 seconds and the Second Pulse Amplitude is less than10% of power level 3 output current. Of note, the resonant frequencywaveform 1925 exhibits sections of both heating (heat flux into theblade) and cooling (heat flux out of the blade). The “minimum latchtime” parameter, defined herein as the minimum amount of time forresponse(s) to a Condition Set X to be triggered, is intended tomaintain triggering of a Response Set during pulsed application (oneexample of a latch time may be about 1 second). Of additional note, asshown in FIG. 42A, the load or impedance waveform 1922 does not dropbelow 200 Ohms throughout the run sequence. This may be favorableconsidering that the impedance waveform 1922 for a marching applicationconsistently drops below about 150 Ohms while operating in air betweencuts implying that an impedance limit may be used for resettingCondition Sets. In one aspect this impedance limit may be used forimplementation of the “low drive in air” concept as disclosed in U.S.Pat. No. 5,026,387 to Thomas.

FIG. 43 is a graphical representation 1932 of a calculated frequencyslope waveform 1934 for the pulsed application shown in FIG. 41 andFIGS. 42A-C plotted on a gross scale. FIG. 44 is a zoomed in view of thegraphical representation of the calculated frequency slope waveform 1934for the pulsed application shown in FIG. 43. Both FIGS. 43 and 44 showthe calculated frequency slope waveform 1934 for the pulsed applicationshown in FIG. 41 and FIGS. 42A-C. Frequency slope (kHz/Sec) is shownalong the vertical axis and Time (Sec) is shown along the horizontalaxis. Two scales are shown, where FIG. 43 shows a gross scale forfrequency slope and FIG. 44 shows a “zoomed in” view. For frequencyslope, the same trends seen under continuous drive are shown in pulseddrive including values that correlate well to heat flux into (negativefrequency slope) and out of the blade (positive frequency slope). Thetransient nature of the frequency curve and frequency slope curve due topulsing, combined with the moving average calculation of frequency slopemake use of the frequency slope curve during pulsing difficult. Of note,the tissue separated at 13 seconds. As can be seen in FIG. 43 andespecially FIG. 44, the rate of cooling can be used to trigger aresponse correlating rapid cooling in the dwell portions of pulsedoutputs to the completion of a tissue transection using logic (not shownby logic flows in FIGS. 20-22) where frequency slope waveform 1934exceeds a threshold value, in this case of about 0.04 kHz/sec whensampled at the ends (i.e., the settled regions) of the dwell periods. Ascan be seen in FIG. 42A, the impedance waveform 1922 can be used totrigger a response correlating high impedance (high resistance tomechanical motion or vibration) to the completion of a tissuetransection using logic (again, not shown by logic flows in FIGS. 20-22)where transducer impedance waveform 1922 exceeds a threshold value, inthis case of about 700 Ohms when sampled at the beginnings (i.e., thesettled regions) of the dwell periods.

FIG. 45 is a graphical representation 1936 of other data waveforms 1938of interest such as impedance, power, energy, temperature. In FIG. 45,the vertical scale to the right applies to the impedance curve only.

The present disclosure now turns to considerations for power level andclamp pressure profile in an ultrasonic instrument. The rate of heatingof a blade to pad interface is proportional to blade displacement,interface coefficient of friction and load (clamp pressure or normalforce). Testing was performed to assess the tissue algorithm at a rangeof displacements (power levels) and device specific combinations ofclamp pressure and coefficient of friction (defined largely by padmaterials and blade coatings).

FIG. 46 is a graphical representation 1940 of a summary of weightedfrequency slope versus power level for various ultrasonic instrumenttypes. Weighted frequency slope (kHz/Sec) is shown along the verticalaxis and power level, device type, and device are shown along thehorizontal axis. The instruments used to generate the data summarized inthe graphical representation 1940 are generally commercially availablewith some exceptions. One test procedure included clamping the device,activating the device for three seconds, and calculating the averagefrequency slope over the full three seconds. Other metrics, however, maybe employed. For most devices, the data summarized in FIG. 46 would beapproximately indicative of the minimum frequency slope value. FIG. 46shows the frequency slope summary data for burn-in testing on shearstype ultrasonic instruments where the instruments were clamped, thenactivated for 3 seconds, then unclamped—the average frequency slope overthe full three seconds of activation was calculated and plotted asshown.

Based on predetermined tests and test data from FIG. 46, the followingfrequency slope thresholds are suggested for the main power levels ofuse with some ultrasonic instruments:

(1) level 5 frequency slope threshold: −0.060 kHz/sec;

(2) level 3 frequency slope threshold: −0.045 kHz/sec;

(3) level 5 frequency slope threshold: −0.070 kHz/sec; and

(4) level 3 frequency slope threshold: −0.050 kHz/sec.

System stiffness includes both blade stiffness (cantilevered beam) andpad stiffness/pad thermal stability. The more differentiated theunloaded (no tissue) system stiffness is from the loaded (clamped ontissue) system stiffness, the more robust the tissue algorithmperformance. Other constraints, of course, may limit system stiffness onthe high end.

Further exploration of displacement effects were analyzed based on alarger set of data. For the ultrasonic system, power levels areessentially differentiated by output current target values and, current,which is proportional to vibratory amplitude or displacement. Analysisof this data also may include digital smoothing of the frequency data toobtain usable frequency slope curves.

FIGS. 47-49 show frequency and current versus time waveforms obtainedusing one embodiment of a generator and an ultrasonic instrument toexcise a porcine carotid artery at power level 5.

FIG. 47 is a graphical representation 1970 of resonant frequency versustime waveform 1972, an averaged resonant frequency versus time waveform1974, and a frequency slope versus time waveform 1976 of one embodimentof a generator. Frequency (kHz) and Frequency Slope (kHz/Sec) are shownalong the vertical axes and Time (Sec) is shown along the horizontalaxis. The frequency slope waveform 1976 is based on the averagedfrequency data and was obtained by post processing the frequencywaveform 1972 data. The raw frequency data is plotted as well assmoothed (via simple moving average) frequency data and frequency slope(calculated from the smoothed data because the raw frequency datacontains stair-stepping due to rounding of the streamed data). Theaverage resonant frequency waveform 1974 is obtained via a 70 msecmoving average (kHz) of the resonant frequency data.

FIG. 48 is a zoomed in view 1978 of the resonant frequency versus timewaveform 1972 and the averaged resonant frequency versus time waveform1974 of one embodiment of a generator. Frequency (kHz) is shown alongthe vertical axis and Time (Sec) is shown along the horizontal axis.

FIG. 49 is a zoomed in view 1980 of the resonant frequency waveform 1972and a current versus time waveform 1982 of one embodiment of agenerator. Frequency in (Hz) and Current (A) is shown along the verticalaxes.

In FIGS. 48 and 49, the respective zoomed in views 1978, 1980 are shownto see the effect of smoothing frequency data and to see riseinformation at the start of the application, which may be helpful forassessment of parameters such as Time to Wait.

Other aspects of the tissue algorithm described herein may be applied tosituations when little to no intervening tissue remains (between theultrasonic blade and the clamp arm) and waste energy is being dumpedinto the end effector. Accordingly, in one embodiment, the tissuealgorithm may be modified to provide feedback to the user relative tothis situation. Specifically, the tissue algorithm leverages the factthat the resonance of an ultrasonic blade changes relative totemperature (decreases with increasing temperature and increases withdecreasing temperature).

In one aspect the tissue algorithm disclosed herein may be employed tomonitor the frequency slope of a waveform where the algorithm monitorsthe change in resonant frequency slope to indicate the changingcondition of the tissue. In the case shown in FIG. 50, for example, theinflection of the frequency response curve correlates to the point atwhich the tissue begins to separate (i.e., there is a tissue tag and theuser continues to activate the instrument), which can be verified byexperimentation. The change in frequency slope can be used to provide anindicator (e.g., distinct beeping sound, flashing light, tactilevibration, among others previously discussed) to the user (that wasteenergy is being dumped into the end effector) or the generator outputcould be controlled or stopped.

In another aspect, the tissue algorithm disclosed herein may be employedto monitor the frequency threshold of a waveform, where the algorithmmonitors the change in frequency as the waveform crosses some thresholdor difference from some known state (e.g., room temperature). Similar tomonitoring the frequency slope, as the change in frequency drops belowsome threshold value or difference, an indication can be given to theuser that the device end effector is heating at an accelerated rate.Again, FIG. 50 provides a graphical illustrative view of a frequencythreshold.

In yet another aspect, the tissue algorithm disclosed herein may beemployed to monitor the frequency slope change and the frequencythreshold in combination. The combination of a significant change infrequency slope and a drop in frequency below some threshold can be usedto provide an indication of high temperature.

Turning now to FIG. 50, is a graphical representation 1990 of normalizedcombined power 1991, impedance 1992, current 1993, energy 1994,frequency 1995, and temperature 1996 waveforms of one embodiment of agenerator coupled to an ultrasonic instrument. As shown, the tissuebegins to separate at 6.672 seconds. From this point until the tissuefully separates, about 55-60% of the total frequency drop is obtained,the temperature increases by a factor of about 1.92 (from 219° C. to418° C.) and about 28% of the total energy applied is delivered. Thelocal slopes of the frequency vs. time waveforms are shown by a firstset of dashed lines 1997, which represents a rapid change in theresonant frequency slope. Monitoring this slope 1997 affords theopportunity to indicate a dramatic change which typically occurs whenthere is limited to no intervening tissue and the vast majority of poweris being applied to the blade/tissue pad interface. Likewise, thefrequency change from its resonance in a known state (e.g., roomtemperature) can be used to indicate high temperatures—a frequencychange threshold is shown with a second dashed line 1998. Also, acombination of these two, frequency slope change and frequency changethreshold, can be monitored for purposes of indication. Note that thefrequency changes in this case from an initial value of 55,712 Hz to anend value of 55,168 Hz with the threshold shown at about 55,400 Hz.

While several embodiments have been illustrated and described, it is notthe intention of the applicant to restrict or limit the scope of theappended claims to such detail. Numerous variations, changes, andsubstitutions will occur to those skilled in the art without departingfrom the scope of the invention. Moreover, the structure of each elementassociated with the described embodiments can be alternatively describedas a means for providing the function performed by the element.Accordingly, it is intended that the described embodiments be limitedonly by the scope of the appended claims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment. Thus,appearances of the phrases “in various embodiments,” “in someembodiments,” “in one embodiment,” or “in an embodiment” in placesthroughout the specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment may be combined, in whole or in part, with the featuresstructures, or characteristics of one or more other embodiments withoutlimitation.

1. A method of driving an end effector coupled to an ultrasonic drivesystem of a surgical instrument, the method comprising: generating by agenerator at least one electrical signal; monitoring the at least oneelectrical signal against a first set of logic conditions; triggering afirst response of the generator when the first set of logic conditionsis met; and determining from the at least one electrical signal aparameter associated with the surgical instrument.
 2. The method ofclaim 1, wherein the determined parameter is an impedance of the endeffector, the method further comprising: resetting the generator whenthe impedance crosses a predetermined threshold.
 3. The method of claim1, wherein the determined parameter is a rate of temperature change ofthe end effector assessed by calculating a frequency slope, the methodfurther comprising: comparing the frequency slope against apredetermined threshold.
 4. The method of claim 3, wherein the rate oftemperature change is a rate of cooling.
 5. The method of claim 3,wherein the rate of temperature change is a rate of heating.
 6. Themethod of claim 1, wherein the determined parameter is proportional to afrequency slope, and wherein it determined parameter is a rate oftemperature change of the end effector.
 7. The method of claim 6,wherein the rate of temperature change is a rate of cooling.
 8. Themethod of claim 6, wherein the rate of temperature change is a rate ofheating.
 9. The method of claim 1, comprising monitoring impedance of atransducer of the ultrasonic drive system in a dwells region duringpulsed activation.
 10. A method of driving an end effector coupled to anultrasonic drive system of a surgical instrument, the method comprising:generating by a generator at least one electrical signal; determiningfrom the at least one electrical signal a parameter associated with theend effector; and comparing the determined parameter against apredetermined parameter.
 11. The method of claim 10, wherein thedetermined parameter is an impedance of the end effector.
 12. The methodof claim 11, comprising resetting the generator when the impedancecrosses a predetermined threshold.
 13. The method of claim 12,comprising monitoring the impedance of the end effector of theultrasonic drive system in a dwells region during pulsed activation. 14.The method of claim 10, wherein the determined parameter is a rate oftemperature change of the end effector.
 15. The method of claim 14,wherein the rate of temperature change is selected from the groupconsisting of a rate of cooling and a rate of heating.
 16. A method ofdriving an end effector coupled to an ultrasonic drive system of asurgical instrument, the method comprising: generating by a generator atleast one electrical signal; monitoring the at least one electricalsignal against a first set of logic conditions; triggering a firstresponse of the generator when the first set of logic conditions is met;and determining a frequency slope of the at least one electrical signal.17. The method of claim 16, wherein the frequency slop is proportionalto a rate of temperature change of the end effector.
 18. The method ofclaim 17, wherein the rate of temperature change is a rate of cooling.19. The method of claim 17, wherein the rate of temperature change is arate of heating.
 20. The method of claim 16, comprising comparing thefrequency slope against a predetermined threshold.